Got some free time, and played through with most things now, so, let's have some insight:
Note, things I have not used will have their names in Italics.
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God Teir [Or, if you prefer HG/SS Scyther Teir]:
Archen - Comes stupidly early for such a powerhouse, avaliable before the 4th Gym, and comes at a respectible level. Godly offensive stats and Flying/Rock STAB takes everything except the Klink and Pawniard lines out. As if that's not insane enough raise it three levels, and it gets a Base 110 STAB.
The only downside, is Acrobatics clashes with the Lucky Egg, but you'll be smashing everything apart anyway, so you don't need the extra EXP.
High Teir:
Oshawott - Despite all three Unova starters, in general, sucking, Oshawott is by far the best of them, and, indeed, is the best in-game Water type. Hell, Revenge makes him a better Fighting-Type than Emboar is until Gym 7.
His all-rounded nature allows him to take on anything decently, unlike Emboar, and his movepool puts Serperior to shame.
He also dosen't suffer against any Gym in particular. He can hold his own everywherw, even hitting Elesa neutral [All three starters suffer against Emolga anyway]
Darumakka - Brute force, that's the best way to describe Darumakka. Best Fire-type in the game, decently fast for in-game, and, especially after evolution, has massive amounts of power.
Drillbur - I might have put it in Mid-High, but it's one of the two pokemon that stand a chance against Elesa. Freakin Emolga. It's a little slow-in game for my tastes, which stops it from really sweeping, but, it's sheer power, and untility against Elesa, as well as very early avaliabilty makes it a good choice.
Sawk - Insane for a Pre-2nd Gym catch, there is really no other way to decribe Sawk. Fast, Strong, and has Sturdy, just in case.
Silygliph - Best in-game special attacker, with the possible exception of Lilligant. Shadow Ball, Air Cutter and Psychic decimate everything.
Petilil - WHO NEEDS TYPE COVERAGE?! Petilil is merely OK when you get it, and of course, Burgh follows up. Then you get Giga Drain, the Sun Stone, and Quiver Dance.
Laugh as everything that isn't Deerling or Afrobull gets swept before you. You don't even need to set up to +6 +6 +6 like some other guy said, +1 will do for 99% of the battles, and +0 is also more than feasable if you're just wanting to murder one thing. Base 110 Sp.Atk is still more than useable out of the box!
Mid-High Teir:
Lillipup - Slows down mid-game and late game, but spikes between then makes it solid still.
Throh - Inferior in-game to Sawk, unless you want to Bulk-Up Sweep
Timburr - See Throh
Sandile - Too frail for my tastes, and horrible initial movepool
Tympole - Great tank, but isn't as good as Oshawott
Scraggy - Too slow, but powerful, and also has the ability to set up rather well.
Joltic - CompoundEyes Thunder is great, as is it's speed, but it's a one-trick pony outside of that, and comes too late in the game, after the 5th Gym.
Klink - Destroys everything except Renbu after you get it, but, like Joltic, comes too late. A late final evolution also hurts, although Klang is more than capable with Evolite, and Klink can sweep Skyla easily with Charge Beam and Automonise.
Mid-Teir
Tepig - Great early on, then slows down massivly from Gyms 3 -> 7. Then, he slows down after that, once more, and dosen't recover.
Maractus - Pretty good alternative Grass-type, especially if you're playing Black.
Pidove - Who cares about it's level up movepool, it makes do until you get to Nimbasa. Then, RETURN. Early Roost as well. Then you get Fly a little bit later. Cheer Up/Roost/Fly/Return is all you need, really. To be frank, it's probobly the 2nd best Normal/Flying regional bird, after Staraptor. Yes, it's BETTER THAN SWELLOW [Mainly due to being able to set up and Roost]
*Everything else in Mid-Teir not mentioned elsewhere remains there*
Low Teir
Basculin - I tried it, I hated it.
Cottonee - Yeah, these teirs are for speedruns. Cottonee =/= speedrun.
Durant - FAR too late
Druggigon - See Durant, also outclassed by Axwe.
Snivy - 2nd worst starter ever. Outclassed by all other Grass-types in the game except Cottonee. It also suffers Chikorita Syndrome, where the world is out to kill Grass-types. Only becomes useful after it gets Coil, and even then, only moderately so. At least it's better than Meganium!
Garbage Teir:
Purrloin - It's so bad it deserves it's own teir, it's THAT much worse than everything else. It's outclassed at being a Dark-type by the other freaking Derps. Even Minezumi! Words cannot describe how horrible Purrloin is in-game. Awful stats, awful movepool, and 100% outclassed from the word go.