Mewtwo @ Life Orb
Timid 252 SpA / 4 SpD / 252 Spe
- Ice Beam
- Fire Blast / Aura Sphere / Flamethrower
- Calm Mind
One thing not mentioned is why people use Aura Sphere. Its not just because Fire Blast is reliant on sunny weather (and when it is its super strong! A 180 BP attack coming from that massive attack stat X_X), its because its Mewtwo's only way of bypassing Tyranitar.
Should Mewtwo forgo Ice Beam, not only will it be walled by Tyranitar, its going to be unable to switch and killed thanks to its access to Pursuit. Besides the only thing you miss out on is hitting Gene / Ferro / Forry / Psychic types (as long as they're in the sun) harder, but granted, I will agree with Tobes when he says that the current state of the Ubers meta means Fire Blast is more important :P.