Originally Posted by U-B-3-R
Easily Metagross. You don't see any Psychic types that are durable defensively like Metagross, yet have a monsterous stat for them attack with combined with a strong STAB move like Meteor Mash. Plus, Metagross makes a pretty nice (possibly suicide) lead.
I have to agree, Metagross is a great Pokémon anyway you think about it.