A Scizor with Aerial Ace is a great idea, considering its high attack stat. I understand that you want to use Scizor to counter fighting types, but bear in mind that Scizor has a 4x weakness to Fire, and think of the popularity of Blaziken and Infernape (and to a lesser degree, Emboar). You have the potential to get screwed pretty hard there if you don't cover your speed stat.
I'd suggest the following EV spread:
252 ATK / 4 Sp. DEF / 252 SPD
In fact, give it a Life Orb, teach it Swords Dance and a few damaging moves, and you've got a serious powerhouse. (I'm not a huge fan of choice items because they limit your pokémon, although feel free to give it a Choice Band instead) Try something like this:
Scizor @ Life Orb
Adamant, Technician
-Aerial Ace (Because you wanted it
; good against fighting types, priority move)
-Swords Dance (Powers up its already through-the-roof attack stat)
-Iron Head or Bullet Punch (for STAB)
-Superpower (Because fighting type moves are super effective against 5 types)