Totally copying Jac's style.
Larvesta - A or B (B)
Larvesta, although it still has the most powerful U-turner in the tier, is unfortunately not A rank any longer. With the fall of gligar, hazards became far more usable, and while all VoltTurners hate hazards, Larvesta despises them, being unable to switch in more than once if rocks are up. It's not fast enough to have it be worth investing in speed unless you plan to run scarf, and with scarf you can't run morning sun, the only way Larvesta can overcome rocks.
With Ponyta as a superior option for burning, unless you really, really care about switching in on ground type moves, Larvesta has a niche on some teams, but is not A-rank material.
Slowpoke - A or B (A)
Despite the Rise of Knock Off™,Slowpoke is still an extremely viable defensive threat in today's meta. The other walls people use are, by and large, normal types such as Munchlax or Lickitung. While normal is by no means a bad typing, Slowpoke's psychic/water typing is still slightly superior in today's meta. Even though psychic makes Slowpoke a bad matchup against Misdreavus, Pawniard, and Murkrow for obvious reasons, and Mienfoo can simply U-turn away to do damage, it's a fantastic wall for Meditite. Although most people might say that Meditite will always run Thunder Punch to deal with Slowpoke, I've found a fairly even split between Fire Punch and it's electric brother, due to the existence of Honedge.
Slowpoke gets two major things that make it a fantastic wall– Regenerator and Slack Off. Slowpoke heals often and well, making it a much more effective wall than others, who have to die when they must take a turn to heal. Slowpoke's movepool also sets it apart from others, as it can not only inflict paralysis on enemies to weak them for the rest of the team, but can also use the uncommon yawn to force a switch, giving slowpoke the chance to heal, set up, or switch. I personally have seen a Belly Drum slowpoke used to great effect, as unlike other users, it can set up under trick room and then switch out after it ends, while not having to use berry juice due to regenerator. I'll be the first to admit that Slowpoke isn't for everyone, but it's still more useful than a B-rank at the moment.
Torchic - A or B (B)
Baton Pass is ew. But in all honesty, Torchic is just not good enough to be used as an A-rank Pokemon. Unless you intend to just send speed boosts to teammates, Torchic is extremely vulnerable during set-up turns, being easily OHKOed. In addition, taunt makes it completely useless if you predict the turn they set up and don't use protect.
Just... No. Protect also makes it set up bait, so it's actually extremely limited to what you can actually prepare to pass on. Fire typing and the stealth rock weakness is just the icing on the proverbial cake. When used right, it's a dangerous threat, but so is Clamperl.
Drilbur - A or B (A)
I feel that Drilbur is actually the most effective anti-lead and hazard remover in the tier. Vullaby has to watch out for Pawniard for defogging (you know, one of the most common Pokemon in the entire tier?), while Drilbur earthquakes, spins, and doesn't afraid of anything. People claim that it's outclassed by Vullaby, but can Vullaby remove the hazard setters? Drilbur can. Dwebble with sturdy? Mold Breaker dgaf. Pretty much all rock setters in general? Either Earthquake or Rock Slide is super effective, even on Pawniard. Your precious Trubbish? Your garbage bag will split open under the wrath of the earth!
But honestly, although Drilbur doesn't have a lot of sets, it's extremely effective at what it does, and can sweep teams that aren't prepared for the revenge of the spinning mole.
Cottonee - A or B (???)
I honestly don't know. I've used it, with mixed results, and seen it used with mixed results. Sometimes it's fantastic, resulting in another team member sweeping after you use memento or something that allows for sweeping, while other times it just gives the opponent a free kill. It's main use, I found, is stopping setup sweeper with encore, but even tirtouga, the main thing it gets used to stop, can aqua jet and get encored into a fairly decent move instead of shell smash. Cottonee has varied from A rank to C rank for me, so I can't speak definitely on it.
Shieldon - C or D (D)
Shieldon sucks and is inferior to pretty much anything that has sturdy. The only thing it has going for it is metal burst and an immunity to poison type attacks. If you really want to abuse sturdy for the purpose of doing more damage, Dwebble gets counter, which is infinitely more useful than Metal Burst considering that knock off is the most popular move in the meta. Then we get things like Drilbur and hazards. When two types are able to murderize you, you're not a very good option at all.
Mantyke - B or C (C)
The special defense is nice, and it makes a decent teammate for chinchou, but its physical bulk and 4x electric weakness aren't fun. At all. Not for many teams, honestly.
Shellder - B or C (C)
I brought this up earlier, you can see my earlier post for full thoughts.
Honedge C or B (C)
The ghost, despite having the best neutral coverage ever, is slow and both Dark and Ghost weak. Even though ghost is the best type, Honedge is just outclassed, unable to really make up for its pathetic special defense, and requiring setup to be fast enough to utilize its attack.
Darumaka- B or C (D)
Why do people even use this thing when you've got so many better fire types out there? If you want to see how lucky you are I guess you could give it a scarf or a band and have it hit like a truck, but Darumaka's frail and sometimes manages to miss the broad side of the barn and then gets killed.
It doesn't even deserve C, frankly.
Lileep - B or C (B)
Use it more. Walls all of the things. I think we can all agree that it's not a C-rank. Of course, I'll list my reasons if someone really wants me to.
Larvesta - A or B (B)
Larvesta, although it still has the most powerful U-turner in the tier, is unfortunately not A rank any longer. With the fall of gligar, hazards became far more usable, and while all VoltTurners hate hazards, Larvesta despises them, being unable to switch in more than once if rocks are up. It's not fast enough to have it be worth investing in speed unless you plan to run scarf, and with scarf you can't run morning sun, the only way Larvesta can overcome rocks.
With Ponyta as a superior option for burning, unless you really, really care about switching in on ground type moves, Larvesta has a niche on some teams, but is not A-rank material.
Slowpoke - A or B (A)
Despite the Rise of Knock Off™,Slowpoke is still an extremely viable defensive threat in today's meta. The other walls people use are, by and large, normal types such as Munchlax or Lickitung. While normal is by no means a bad typing, Slowpoke's psychic/water typing is still slightly superior in today's meta. Even though psychic makes Slowpoke a bad matchup against Misdreavus, Pawniard, and Murkrow for obvious reasons, and Mienfoo can simply U-turn away to do damage, it's a fantastic wall for Meditite. Although most people might say that Meditite will always run Thunder Punch to deal with Slowpoke, I've found a fairly even split between Fire Punch and it's electric brother, due to the existence of Honedge.
Slowpoke gets two major things that make it a fantastic wall– Regenerator and Slack Off. Slowpoke heals often and well, making it a much more effective wall than others, who have to die when they must take a turn to heal. Slowpoke's movepool also sets it apart from others, as it can not only inflict paralysis on enemies to weak them for the rest of the team, but can also use the uncommon yawn to force a switch, giving slowpoke the chance to heal, set up, or switch. I personally have seen a Belly Drum slowpoke used to great effect, as unlike other users, it can set up under trick room and then switch out after it ends, while not having to use berry juice due to regenerator. I'll be the first to admit that Slowpoke isn't for everyone, but it's still more useful than a B-rank at the moment.
Torchic - A or B (B)
Baton Pass is ew. But in all honesty, Torchic is just not good enough to be used as an A-rank Pokemon. Unless you intend to just send speed boosts to teammates, Torchic is extremely vulnerable during set-up turns, being easily OHKOed. In addition, taunt makes it completely useless if you predict the turn they set up and don't use protect.
Just... No. Protect also makes it set up bait, so it's actually extremely limited to what you can actually prepare to pass on. Fire typing and the stealth rock weakness is just the icing on the proverbial cake. When used right, it's a dangerous threat, but so is Clamperl.
Drilbur - A or B (A)
I feel that Drilbur is actually the most effective anti-lead and hazard remover in the tier. Vullaby has to watch out for Pawniard for defogging (you know, one of the most common Pokemon in the entire tier?), while Drilbur earthquakes, spins, and doesn't afraid of anything. People claim that it's outclassed by Vullaby, but can Vullaby remove the hazard setters? Drilbur can. Dwebble with sturdy? Mold Breaker dgaf. Pretty much all rock setters in general? Either Earthquake or Rock Slide is super effective, even on Pawniard. Your precious Trubbish? Your garbage bag will split open under the wrath of the earth!
But honestly, although Drilbur doesn't have a lot of sets, it's extremely effective at what it does, and can sweep teams that aren't prepared for the revenge of the spinning mole.
Cottonee - A or B (???)
I honestly don't know. I've used it, with mixed results, and seen it used with mixed results. Sometimes it's fantastic, resulting in another team member sweeping after you use memento or something that allows for sweeping, while other times it just gives the opponent a free kill. It's main use, I found, is stopping setup sweeper with encore, but even tirtouga, the main thing it gets used to stop, can aqua jet and get encored into a fairly decent move instead of shell smash. Cottonee has varied from A rank to C rank for me, so I can't speak definitely on it.
Shieldon - C or D (D)
Shieldon sucks and is inferior to pretty much anything that has sturdy. The only thing it has going for it is metal burst and an immunity to poison type attacks. If you really want to abuse sturdy for the purpose of doing more damage, Dwebble gets counter, which is infinitely more useful than Metal Burst considering that knock off is the most popular move in the meta. Then we get things like Drilbur and hazards. When two types are able to murderize you, you're not a very good option at all.
Mantyke - B or C (C)
The special defense is nice, and it makes a decent teammate for chinchou, but its physical bulk and 4x electric weakness aren't fun. At all. Not for many teams, honestly.
Shellder - B or C (C)
I brought this up earlier, you can see my earlier post for full thoughts.
Honedge C or B (C)
The ghost, despite having the best neutral coverage ever, is slow and both Dark and Ghost weak. Even though ghost is the best type, Honedge is just outclassed, unable to really make up for its pathetic special defense, and requiring setup to be fast enough to utilize its attack.
Darumaka- B or C (D)
Why do people even use this thing when you've got so many better fire types out there? If you want to see how lucky you are I guess you could give it a scarf or a band and have it hit like a truck, but Darumaka's frail and sometimes manages to miss the broad side of the barn and then gets killed.
It doesn't even deserve C, frankly.
Lileep - B or C (B)
Use it more. Walls all of the things. I think we can all agree that it's not a C-rank. Of course, I'll list my reasons if someone really wants me to.