Well, I've just beaten Ghetsis, and although I only used a team of 4, and I've Audino grinded quite a bit, here's my thoughts on what I used:
Tepig was quite mediocre for a Fire starter overall, but it was very helpful despite that. Once it gets Flame Charge it DOMINATES for quite a while into the 20s, but honestly, having Arm Thrust as your only form of STAB until Mistralton at the very least is very annoying, since you have to rely on a coin toss to beat some of the stronger foes. From there it sadly faded into mediocrity until it got Heat Crash, but when it evolved it became very effective and strong, and when it got Hammer Arm it was even more so. Late game it was very helpful and decimated Ghetsis (HYDREIGON OHKOED WITH HAMMER ARM DESPITE EMBOAR BEING 2 LEVELS LOWER. WHAT A BOSS.) and 2 of the Elite 4, but overall, it's performance wasn't that great, so I believe it should go in
MID, although if there is a tier split I recommend it in Upper Mid, since it is effective late game.
This thing has gotten a lot of smack in this thread, but honestly having tried it solely because of its utility in hunting shinies, I chose it, and it was surprisingly very good! It had surprisingly good Attack and learning Crunch at level 16 really helps it in killing off enemies. Unfortunately since I stupidly gave it Cut it had subpar STAB until Mistralton, but even then it was effective with just Cut and Crunch, and its catching skills are second to none. It falters a LOT lategame, especially against the E4 and N/Ghetsis, though, which is why it should stay in
MID, but Upper Mid if the tiers change.
Now this thing is CRIMINALLY underrated. I caught it in Pinwheel Forest looking for another team member, and although it started out crap, by the time it got Poison Tail and Bug Bite, it was KICK-ASS and managed to hold it's own very well. When it evolves into Whirlipede, it gets a lot of bulk and is very useful, although losing use at the desert, but when it evolves into Scolipede... My god, it singlehandedly became my best team member, even when Emboar and Watchog were fully evolved! Mine had a Relaxed nature, but it still had high speed and good attack to use throughout the game, and when Mistralton came around, I got Steamroller and Megahorn (from the move relearner) and it teared apart everything it went up against, even in the Elite 4, where Caitlin and Grimsley were demolished without a trace. Considering all this, I REALLY wanna push this guy for
HIGH (especially if Sandile is in there), because this thing just frigging RAPES, but it has a weak start, so if anything it should be in
Upper Mid if the tiers get split.
Ooh boy, this guy. Let me just say that Ferroseed is one of the HARDEST THINGS TO TRAIN in Pokemon history, EVEN WITH AUDINO ALL OVER THE PLACE. Its level up moves are initially poor, and its typing is offensively very bad as well. I really struggled training this thing up, but I persevered and when it evolved into Ferrothorn before the 6th gym, I wasn't disappointed in the slightest. The gain of Power Whip was a godsend to this thing, and throughout the game since then I've been using it so much it's unbelievable. Curse up and then either Gyro Ball or Power Whip as you please, as well as having additional Iron Barbs damage! Gyro Ball admittedly has poor PP, but if you're gonna use Ferrothorn, you'd want to have PP Ups ready to make it a more viable move. Ferrothorn basically soloed Brycen (I wanted to see what it could do, it wrecked), Drayden, Caitlin (Megahorn missed Musharna :( ) and N (except Zoroark, fucking punk had Flamethrower), as well as helping out greatly against Shauntal and Ghetsis. It's endgame utility is AMAZING, but when you get it, it's crap. Perfect candidate for
MID IMO.
Like I said, that's just my two cents as I played through the game, if anybody wants to ask why I base my opnions, then don't hesitate to do so!
NOTE: Before anyone asks, I deliberately played through Black whilst ignoring so called powerhouses like Darumaka, Archen and Sigilyph. I did these because I wanted the game to be interesting and I wanted to test whether some of the lower Pokes on this list can actually be useful. I've been stalking this thread for a few months haha!