Hoothoot - C- It's completely outclassed by Staraptor, even in bulk after factoring in Inimidate. And Close Combat > Psychic.
Spirtomb - D - You have to do a rather long sidequest underground to battle it, and even then, it's offensive ability isn't much better than Bronzong.
Wooper - C- It's roughly equal to Gastrodon, same type, not much difference in movepools.
Wingull - D - Wingull is fast and weak, Pelliper is slow, bulky, and weak. For Surf, use Gyarados, for Fly, use Starly.
Girafarig - C - It's stats aren't bad, and it's avaliable after the 4th Gym. However, other Psychic and Normal types outclass it, and it's past the gym where it would have been most useful (Fatina).
Hippopotas - C - Tanks are generally poor in-game, and Hippowodon, while packing a punch, is SLOW, and weak on the special side of things. Not to mention to Unown side-quest to get it.
Azurill - C - Azurill is useless, Marill is useless, and Azumarril is of moderate use, but still outclassed.
Skorupi - C - One weakness is nice, but it's hard to find in the Safari Zone, and leveling such as weak pre-evo to 40 is overkill. Although, if you catch it as a Drapion, it's B rank.
Croagunk - B - Decent typing, good stats, and is amoung the faster Fighting-types in the game. Toxicroak is decent in general, especially with STAB Toxic Jab and 'Insert Fighting Move of Choice here', along with a somewhat decent movepool. However, in terms of sheer power, go for other fighting-types.
Carnivine - D - If you WANT a grass type at the 5th Gym, go with Tangla, or Budew.
Remoraid - C - God of movepools concerning beam-type moves, and Octillery boasts of Base 105 attack stats. However, such a low speed is nothing to be proud of. Remoraid may have the speed, but not the power.
Finneon - D- - Luvdisk of the 4th Gen. Enough said.
Tentacool -B- Thankfully, they can be caught at around lv 30, when you have surf. Tentacruel is about the best specialy based water type in-game bar Emploeon. Late avaliabilty is what's keeping it at B.
Mantyke - D - I'm not waiting for the 8th badge to catch a weak baby pokemon, that needs a Remoraid to evolve into something outclassed by my Gyarados.
Snover - C - Avaliable far too late in the game, as with all the Ice-types... in EVERY GAME. Sure, you can catch Abomasnow, but if you must have an Ice type, use a Mamoswine.
Manaphy - E - Not avaliable in the main game.
Gligar - C - Gligar is bad unless you get TM Earthquake, but in that case, you'd have a Gible. Gliscor is decent in-game, but it's still outclassed by Gible.
Nosepass - D - Early catch, high defences early evolve, due to you being in Mt Coronet when you catch it, dreadful speed, dreadful attack power. Outclassed by other Rock types, and Steelix outclasses Probopass.
Ralts - B - Avaliable somewhat early. Ralts and Kirlia are lacking somewhat, but both Gardevoir, who is a fast evolution, and could be gotten before the 4th Gym, and Gallade, who comes a little late without a lucky pickup, are good pokemon to use, with wide movepools, some bulk, and high power. Late Gallade, and the weak start is what's keeping this as a B.
Lickitung - C - Nothing special statwise, and a bad level-up movepool. Although, if you can get Lickylicky to learn Power Whip, it becomes somewhat useful.
Eevee - A - Get it, and get Vaporeon, as in-game, Vaporeon is the best Eveelution, hands down. Although, keep as Eevee before you get Surf, as Vaporeon will be making do with Quick Attack and Bite until then, and Eevee hits harder with Quick Attack, which is Base 80 for it, due to it's ability.
Swablu - C - Only other dragon bar Gible, but it's the weakest final-stage dragon in the whole game (Only one in UU). Somewhat late catch. Outclassed by Starly and Gible.
Togepi - D - Togepi and Togetic are not worth it.
Houndour - B - Evolves somewhat quickly. Houndoom's movepool isn't godly, but it'll do, with Flamethrower by level, Dark Pulse, high sp.attack, and high speed, as well as Thunder Fang at the move tutor.
Magnemite - A - Evolves almost instantly after getting it. Magnezone is somewhat sub-par, unless you use TM's, such as Shock Wave, Flash Cannon, and Thunderbolt on it. You may want Discharge, due to it hitting everything in double battles, in which case, save TM Thunderbolt, and use Shock Wave, which will do until you learn Discharge.
Tangela - B - Tangrowth has high stats, barring special defence and speed. It's movepool isn't bad either.
Yanma - C - Bad movepool, anything decent is at a late level.
Tropius - B - The 2nd HM Slave, as with Bidoof, they can use all of them. Poor for everything else though.
Rhyhorn - C - 2nd slowest evolution in the game, at a mind-bending lv 42. Ryhdon, and Rhyperior aren't anything special, or worth the grind.
Duskull - C - Poor offence, cannot evolve into Dusknoir until post-game, due to lack of Reaper's Cloth.
Porygon - B - Avaliable quickly, decent sp.attack, both Porygon 2, who you can get instantly, and Porygon Z are great in their own rights.
Scyther - A - Scyther is useful in it's own right, until the 6th Gym, when you'll get Scizor. Scizor is still useless there, but it's great almost everywhere else.
Elekid - D - Comes too late. Great movepool, but just not worth it.
Magby - C - Inferior to Houndoom, and caught later, but a wider movepool.
Swinub - C - Alongside Froslass, possibly the best Ice Type in the game. Swinub is a pain, but Mamoswine is worth it, and might give even Gible some contention for it's spot, due to STAB Ice Shards from Base 130 Attack. It comes FAR too late in the game, however, like all of the Ice-types... in every game.