Surfer, Surfer, Heralds, Thanos alone. Those are the winners. They are more than capable of killing the pilots without needing to wreck the whole mech. Some of the scenarios though they can actually annihilate the whole mech with raw power. Just maybe not Scenario 4 given TTGL's ridiculous size.
Because they have cosmic awareness and are telepaths on top of that, almost all of them. But I think if the pilots were not needed it would be better. Still round for round the cosmics take it even then, but I'd have to think through a few details in the first 3 rounds. Round 4 is certain either way. Thanos can't be put down by TTGL. Zeus is arguable too.
@MarioRedfield: Don't really think that's the case for Arc Gurren. Don't know about SGGL i only saw the movies and he wasn't in them and yeah TTGL certainly is, hell the guy makes Galactus look like a midget.