Hello everyone!
Take a wild guess as to why I chose to create thread on Water-types.
Anyways, while Pokemon like Gorebyss and Huntail might be the most controversial Water-types out there, you can never forget about all the other ones in the type with the most amount of Pokemon in the game in the largest tier.
Obviously, the descriptions are not completely done, but the basic ideas are there.
The obvious ones
Gorebyss may have been unanimously declared Not Broken in the last suspect test, but that in no way makes her any less of a top-tier threat. Gorebyss undoubtedly shaped the metagame to a point where it actually might be somewhat difficult to set up a Shell Smash, but if it does... Do you have a Scarfer over base 85, Absol, Lapras, or Jynx? No? You're doomed.
Huntail isn't nearly as common or as effective as Gorebyss, but that doesn't mean it should never be considered over the feminine counterpart. Huntail is a much greater mixed sweeper than Gorebyss, and can actually become harder to stop after a Shell Smash, as its great mixed attacking stats allow it to muscle past many pokes that would otherwise wall anything it can do.
Carracosta may be the lesser of the three Smashers, and plays more like mixed Huntail than Gorebyss. Due to Carracosta's STAB Stone Edge, it gains the ability to completely demolish Pokemon who could counter Gorebyss like Jynx without a problem as its primary STAB move.
The less obvious one
Due to the existence of DeepSeaTooth and DeepSeaScale, Clamperl can either have monstrously high SpA or SpD (respectively) that it can abuse to either hit even harder than Gorebyss can or take many more hits from special attackers, allowing Clamperl to get off more attacks
The other common offensive ones
Great offensive typing, Swords Dance, a great coverage attack in Megahorn, awesome priority in Aqua Jet, and decent defenses, which is of course backed by very good offensive stats, makes Samurott the most dangerous Swords Dancer in the tier, and can easily dismantle a weakened team.
Its TropiOUs' secret lover, and its stats are deceptive of its actual success. Once put in Rain, Swanna is able to spam STAB Hurricane and STAB Surf, an unresisted combination in NU. Swanna's Speed is also very high for the tier, being able to outspeed common pokes like non-Scarf Jynx and demolish it with Hurricane before it has a chance to do anything. Don't let its seemingly low offensive stats fool you.
The bulky bros
Alomomola's gargantuan HP stat, coupled with its good Def stat, makes it not only the best Wish passer in the tier, but a reliable counter to many of NU's top physical threats, like Swellow and Sawk, but unfortunately can't use Scald due to its absolutely pitiful 40 base SpA.
Another bulky Water-type with giant HP stats? Lapras can work wonders as a full-on special tank, a mixed tank, or even a physical attack. However you look at it, Lapras is one of the best counters to Gorebyss, being immune to Surf, 4x resisting Ice Beam, and being able to take HP Grass and retaliate.
Heeeeeerp. Now that that's out of the way, Quagsire is another amazing bulky Water in NU, being able to easily counter almost any and all physical threat due to Unaware, and can easily spam Recover while the opponent is slowly whittled down by Toxic or Burn. Sure, the 4x weakness to Grass hurts, but that fact can't deter this little fish... thing!
And then, out of nowhere, Seadra. What makes this thing so useful? Eviolite, Eviolite, and more Eviolite. It may miss out on Leftovers, but its as physically defensive as the likes of Alomomola, and should not be sold short, especially when it has a chance to survive a +2 Leaf Blade from Jolly Leafeon. Its 95 base SpA means that its Scalds and Ice Beams will actually leave a dent in the opponent outside of burn. What's more? It has access to Disable.
The Rapid Spinners
If you've played NU for more than 5 minutes, you should be more than aware that the selection of Rapid Spinners, quite frankly, sucks. Regardless, Wartortle can still reliably spin away entry hazards. Unfortunately, Wartortle can easily be turned into set-up fodder with incredibly weak Scalds being its only method of attack.
Staryu is admittedly not as good as Wartorle, but its higher Speed and access to reliable recovery do give it a bit of an upper hand.
The other guys
Floatzel's stats are quite deceptive. It does have blistering Speed (its the fastest Water-type in NU, and tied for fastest in the game bar Arceus) and higher Attack then Samurott, but it simply lacks the punch Samurott has, as its paper bulk gives it no time to set up, and it doesn't even have access to Swords Dance. It does have access to Switcheroo, which can easily cripple something like Alomomola.
Boom. Headshot Smash. But seriously, even off of 90 base Attack, a Choice Banded STAB Head Smash will decimate almost anything in its path. Relicanth also has great defense, making him a great check to the birds.
If you're running a Rain team, Golduck can spam Life Orb/Choiced Rain-boosted Hydro Pumps, and, if you manage to actually hit with Hydro Pump, it can actually do a lot of damage to an unprepared teams.
Base 130 Attack? Check. Really good Defense to go along with it? Check. Almost no Special Bulk? Check. Movepool that isn't impressive at all? Check. Has to compete with Samurott? Double check.
FUCK YEAH SEAKING!!!
... There's not much else to say. Lightningrod's cool I guess, but Seaking still just plain sucks.
It's the largest Pokemon in the entire game, and the most notable thing it does is have inappropriate relations with Skitty. It can use Choice Scarf Water Spout, but its still pretty slow... and it can't do anything else.
Simipour is actually not that awful. It can set up Nasty Plots and proceed to fire off powerful Hydro Pumps, but, unfortunately, Gorebyss does this much better with Shell Smash.
While at first looking absolutely harmless, Choice Band, dual-STAB boosted Waterfalls off of 92 base Atk hurt. Unfortunately, it can't break through any of the walls that plague others like it like Samurott or Huntail, and is an inferior option.
THE GOD OF EVERYTHING!
This deity needs no introduction. When you see your opponent has one, might as well just forfeit now. It will mercilessly kill you and your family. In your sleep. After it burns your house down. After eating everything you love.
Take a wild guess as to why I chose to create thread on Water-types.
Anyways, while Pokemon like Gorebyss and Huntail might be the most controversial Water-types out there, you can never forget about all the other ones in the type with the most amount of Pokemon in the game in the largest tier.
Obviously, the descriptions are not completely done, but the basic ideas are there.
The obvious ones

Gorebyss may have been unanimously declared Not Broken in the last suspect test, but that in no way makes her any less of a top-tier threat. Gorebyss undoubtedly shaped the metagame to a point where it actually might be somewhat difficult to set up a Shell Smash, but if it does... Do you have a Scarfer over base 85, Absol, Lapras, or Jynx? No? You're doomed.

Huntail isn't nearly as common or as effective as Gorebyss, but that doesn't mean it should never be considered over the feminine counterpart. Huntail is a much greater mixed sweeper than Gorebyss, and can actually become harder to stop after a Shell Smash, as its great mixed attacking stats allow it to muscle past many pokes that would otherwise wall anything it can do.

Carracosta may be the lesser of the three Smashers, and plays more like mixed Huntail than Gorebyss. Due to Carracosta's STAB Stone Edge, it gains the ability to completely demolish Pokemon who could counter Gorebyss like Jynx without a problem as its primary STAB move.
The less obvious one

Due to the existence of DeepSeaTooth and DeepSeaScale, Clamperl can either have monstrously high SpA or SpD (respectively) that it can abuse to either hit even harder than Gorebyss can or take many more hits from special attackers, allowing Clamperl to get off more attacks
The other common offensive ones

Great offensive typing, Swords Dance, a great coverage attack in Megahorn, awesome priority in Aqua Jet, and decent defenses, which is of course backed by very good offensive stats, makes Samurott the most dangerous Swords Dancer in the tier, and can easily dismantle a weakened team.

Its TropiOUs' secret lover, and its stats are deceptive of its actual success. Once put in Rain, Swanna is able to spam STAB Hurricane and STAB Surf, an unresisted combination in NU. Swanna's Speed is also very high for the tier, being able to outspeed common pokes like non-Scarf Jynx and demolish it with Hurricane before it has a chance to do anything. Don't let its seemingly low offensive stats fool you.
The bulky bros

Alomomola's gargantuan HP stat, coupled with its good Def stat, makes it not only the best Wish passer in the tier, but a reliable counter to many of NU's top physical threats, like Swellow and Sawk, but unfortunately can't use Scald due to its absolutely pitiful 40 base SpA.

Another bulky Water-type with giant HP stats? Lapras can work wonders as a full-on special tank, a mixed tank, or even a physical attack. However you look at it, Lapras is one of the best counters to Gorebyss, being immune to Surf, 4x resisting Ice Beam, and being able to take HP Grass and retaliate.

Heeeeeerp. Now that that's out of the way, Quagsire is another amazing bulky Water in NU, being able to easily counter almost any and all physical threat due to Unaware, and can easily spam Recover while the opponent is slowly whittled down by Toxic or Burn. Sure, the 4x weakness to Grass hurts, but that fact can't deter this little fish... thing!

And then, out of nowhere, Seadra. What makes this thing so useful? Eviolite, Eviolite, and more Eviolite. It may miss out on Leftovers, but its as physically defensive as the likes of Alomomola, and should not be sold short, especially when it has a chance to survive a +2 Leaf Blade from Jolly Leafeon. Its 95 base SpA means that its Scalds and Ice Beams will actually leave a dent in the opponent outside of burn. What's more? It has access to Disable.
The Rapid Spinners

If you've played NU for more than 5 minutes, you should be more than aware that the selection of Rapid Spinners, quite frankly, sucks. Regardless, Wartortle can still reliably spin away entry hazards. Unfortunately, Wartortle can easily be turned into set-up fodder with incredibly weak Scalds being its only method of attack.

Staryu is admittedly not as good as Wartorle, but its higher Speed and access to reliable recovery do give it a bit of an upper hand.
The other guys


Boom. Head

If you're running a Rain team, Golduck can spam Life Orb/Choiced Rain-boosted Hydro Pumps, and, if you manage to actually hit with Hydro Pump, it can actually do a lot of damage to an unprepared teams.

Base 130 Attack? Check. Really good Defense to go along with it? Check. Almost no Special Bulk? Check. Movepool that isn't impressive at all? Check. Has to compete with Samurott? Double check.

FUCK YEAH SEAKING!!!
... There's not much else to say. Lightningrod's cool I guess, but Seaking still just plain sucks.

It's the largest Pokemon in the entire game, and the most notable thing it does is have inappropriate relations with Skitty. It can use Choice Scarf Water Spout, but its still pretty slow... and it can't do anything else.

Simipour is actually not that awful. It can set up Nasty Plots and proceed to fire off powerful Hydro Pumps, but, unfortunately, Gorebyss does this much better with Shell Smash.

While at first looking absolutely harmless, Choice Band, dual-STAB boosted Waterfalls off of 92 base Atk hurt. Unfortunately, it can't break through any of the walls that plague others like it like Samurott or Huntail, and is an inferior option.
THE GOD OF EVERYTHING!

This deity needs no introduction. When you see your opponent has one, might as well just forfeit now. It will mercilessly kill you and your family. In your sleep. After it burns your house down. After eating everything you love.