Ok, just finished, so I'll give a synopsis on the pokemon that I used.
Flareon: This guy gets jack shit movepool-wise. Even Fire Punch could make it decent, for god's sake. Lacking that, you're forced to use either Fire Fang or Fire Blast as STAB. Have fun using Flareon! It's not a good mon at all and I dropped it after gym 8 because I was tired of dragging it around. Low or Bottom.
Sneasel: I used this guy over Flareon. It doesn't dissapoint; I'd imagine that it plays like Mamoswine (granted, a lot more frail) with a setup move. Ice Punch can be tutored with the free shards and Night Slash is a remember move once you get Weavile (essentially when you beat Marlon; before that, it's stuck with Punishment/Faint Attack, which isn't bad). It takes very little work to become a relevant member of the party, hits hard as fuck, and has a pretty nice offensive typing / Speed. I can't say where it goes since it's so late (ala Piloswine), but Mid suits it well, I guess, since it really does do a lot of work once you get it.
Petilil: I dropped Flareon before the final Achroma fight. I realized that I'd made a mistake in doing so when I started battling him and realized, "Oh shit, I have nothing to hit Steel-types SE". No problem. Just set up 6 QDs on Magneton... and then swept, finishing with no damage but 10 lost pp from Giga Drain. God, this thing is amazing. It gets its full moveset by level 28, evolves at 26 (giga drain)... It's wonderful. (for those curious, the time as a Petilil is pretty OK too). Oh, and last question - anybody with Black 2 want to test out Route 4 Modest max SpA IV trade petilil? It seems really tantalizing). Anyway, High.
Frillish: Although it's a late get, it's quite good with respect to movepool and typing (as I've mentioned before, you already have 3 great HMs/TMs to give it in the form of Surf, Shadow Ball, and Will-o-wisp). Mine had a Special Attack lowering nature, which was unfortunate and it always felt like it missed out on KOes, but beyond that, it was pretty fun to use. If you're lategame and without a Water-type, try using Jellicent and I doubt you'll be disappointed. Mid.
Dunsparce: Dunsparce was really loved by the movepool changes in this game. Ancientpower is surprisingly nice on such a silly Pokemon and can win you games if you get Serene Grace (again, as I've said before, Run Away is, overall, the better ability because Serene Grace's sole use is for Ancientpower). It gets Roost and Coil by level; guess what you can do with the two moves? That's right! Sweep Grimsley, of course (sidenote, his Liepard can't 2HKO you with one crit from Night Slash). Coil gets you out of a lot of seemingly hopeless situations and, funny as it may be, it can win games. Dunsparce is slow and a bit lacking in power though, so Mid suits it well.
Zoroark: Dark Pulse starts to show its worth later in the game. Anyway, High or Top as others have said; it was the highest level in my party at level 60 after the Elite Four for a good reason (plus, it sweeps two Elite Four members with minimal support, which is cool).
Nosepass: Although I wasn't able to use it much in the Elite Four, it was a neat little mon to abuse. Essentially, it's Magnezone-lite; it has that nice steel-typing and a movepool reminiscent of that of Magnezone. It's really not as bad as it may look; it doesn't die very often at all and it does enough damage that it's not embarassing. Earth Power and Discharge are nice coverage moves. Mid.
Some things I'd like to see other people test out:
Pretty much everything outside of Rebirth Mountain (Skarmory, Camerupt, Drifblim, and Skorupi (NOTE: If you're going to try this one, for the sake of your own sanity, get one in doubles grass for a faster evolution))
Cottonee (non-trade)
Traded Cottonee, Petilil, GIGALITH, Tangrowth (for the sake of your own sanity, don't try catching a Mantine; get a Mantyke to evolve instead)
Ampharos (I haven't seen anybody talking about it... don't forget that Electro Ball is better than Thundershock!)
Magby / Elekid
