I'm leaning towards Top for Sandile. Its main downside is that it's pretty frail and not very strong when you first get it (mine had a Lonely nature, so that may have made the first problem worse). It has awesome power, and as Krookodile, it's a nuke. Its coverage is outstanding, and while its bulk and typing aren't exactly good, it can usually survive a moderately powered hit to 2HKO and get the Moxie boost if need be. Speaking of which, Moxie is absurdly cool. The fact that Krookodile doesn't need its whole movepool is really helpful too; having it as a Strength user was really convenient, and Crunch/EQ/Rock Slide did the job just fine.
I know there was a huge debate over Azurill, but I just don't see it as a mid-tier Pokemon. It's a complete wrecking ball throughout most of the game. It lags a fair amount in the endgame, I'll admit to that, but it's an amazing failsafe. If you need a Pokemon who will survive a hit and OHKO back (yes, Azumarill is surprisingly bulky), Azumarill gets it done. Mine lived through 2 Hydreigon Dragon Pulses (it only would have needed to live through 1 if I'd used Superpower, but I thought Ice Punch would KO...not quite), so I didn't have to worry about Hydreigon, which was really convenient. I don't know how it does in BW2, but for example, Oshawott didn't perform as well for me in BW1 as Azurill did in BW2. I don't want to start a debate; that was just my experience with it.
Given how amazing Lucario is, Riolu was surprisingly disappointing. I think it's still high tier; it can sweep all sorts of things quite comfortably, and Grimsley was just the easiest match ever. But I didn't really like its coverage very much in the endgame; Rock Slide wasn't quite strong enough, and since mine was Adamant, I doubt Shadow Ball or something like it would have done much better than Return/Extremespeed (used as a failsafe, since priority is sometimes cool). That said, +2 Close Combat is incredibly, and Return is usually a good enough backup. The problem is that Lucario dies anything supereffective (and it has plenty of weaknesses), so you may have trouble getting that crucial Swords Dance.
Axew is just right in High tier. It's the best late-game Pokemon I've ever used; it easily manages one Dragon Dance, then kills everything at +1. It doesn't even need anything for a coverage move; I had fun with False Swipe and Cut. That said, it comes pretty late and is only "pretty powerful" (not "impossibly powerful") as Fraxure. Fraxure, by the way, is a great candidate for Eviolite. And, as a side note, going through the whole big lead-up scene to Kyurem-B, just to outspeed and OHKO with a Haxorus Dragon Claw is hilarious. I used a Dragon Gem to be safe, but Draco Plate probably would have done the job.
Snivy is also just right; it's so incredibly disappointing a lot of the time, but it sets up with ease on a ton of physical attackers. My team didn't like taking powerful hits from Marshall at all, but Snivy just set up on Throh (thanks, Leech Seed!) and lol'd its way through the rest of the team. If it didn't do that job so well, it would suck horribly. Grass is a terrible, terrible type. That said, I could see Calm Mind with Dragon Pulse doing a good job at covering some of those problems, Flying and Dragon types in particular.
Litwick is awesome. It's good enough late-game to make up for how horrendously bad it is until level 42. I didn't try using it against Marshall (see Snivy), but I wouldn't recommend it; I don't think Psychic is quite powerful enough, and it will die to Rock-type moves. But against anything without a supereffective move, or anything slow and not-super-bulky it can hit supereffectively, it's pretty awesome.