Blaziken- With access to Speed Boost, it can out-speed anything by using Protect and it packs a serious punch with 120 Att, and if you manage to use Swords Dance, it's basically game over.
Greninja- One word, Protean. Protean changes the user's type to the type of the move it uses, meaning it always has STAB and is nearly impossible to predict. (not to mention it's 122 Speed and 103 SpA.)
Venusaur (mega)- This thing is bulky as hell. 120 SpD and 123 Def mean you can easily set up Substitue and Leech seed, Thick Fat is an excellent ability for this tanky Pokemon, it makes Ice and Fire attacks only do neutral damage leaving it with only 2 weaknesses.