Zorua: low tier. It took forever to level up, and now that it's level 50 nearing endgame it's still dying to stupid stuff like level 39's in victory road. It's defenses are ass, its typing is poor and its offensive moves are Night Slash, Shadow Ball and Focus Blast. It usually takes two of these moves to kill anything even if I'm 10 levels higher and one strong attack and Zoroark's dead. The only reason it might even barge into mid is if you use the Level 50 event instead so you have Bark Out, as well as because one Nasty Plot (level 54) and you can actually solo 3/4 of the elite four because of how their typing is in this game. Otherwise, awful for everything else
Virizion/Terakion: low-mid and low respectively. I can't find anything useful to do with these guys. Sacred Sword runs out quickly and even then it doesn't hit that hard. I caught a level 30 Kojondo that's more reliable. I haven't tried Cobalon yet, which I assume might be better since it's caught way earlier than Terakion and has Iron Head instead of shitty ass grass moves, as well as the availability of Flash Cannon.
Genies: first run I'm on black so I have the shittiest - Tornelos. Whatever, Air Slash comes at a reasonable time and there are a lot of good TM special moves that are available in these games (Focus Blast, Grass Knot). Plus he's my fly bitch. Hits hard, typing is okay, I'd put him in Mid since he comes at level 40 and only needs two levels before he can start contribute in the Elite Four. Sure he comes late, but he's one of those pokemon that tops off your party instead of trying to level up near the end. He wasn't all that hard to catch either - however you can only catch him in the mornings (maybe afternoons). I was patrolling Route 5/Raimon gate, took him down to 1hp with one thunderbolt, saved, patrolled some more, took 3 quick balls and roughly 10 minutes to catch him.