1- the master
who better to lead a villainous squad than someone who has brought the world to its knees with intellect rivalling the doctor? Not only can he regenerate but he found yet another way to cheat death through horcruxes, with the master as leader, plan A is all this suicide squad will need.
The "merc with the mouth" not only does he have the skill and ability (not to mention creativity) to kill you before you blink, he has super regenerative powers making him not only hard to survive but even harder to kill.
3- dark willow
with the darkest of ancient power flowing through this "big bad" you wouldn't want to provoke her apocalyptic rage, the only way to keep her nullified is with love, if she's with this squad though I'd say she's all out of love.....
last but by no means least is sylar, driven by the need to be an all powerful being just to be special, he has no qualms in killing whoever he needs to in his path to achieve his goal of supremacy. Being cunning, devious and with multiple powers to aid this squad in any situation, plan A just became plan A*