I like ALL of these moves because they're all great. I think I'll choose EARTHQUAKE because in a 2-on-2 battle, if your partner has levitate or is a flying type, you could really put a large dent in your opponent's team.
Substitute, Focus Punch, Leech Seed, Mega Horn, Thunderbolt, Ice Beam, Crunch, Sludge Bomb, Dragon Dance and Sword Dance are my favourite popular moves.
Personal favourites are Silver Wind, Perish Song, Magical Leaf, Water Pulse, and Aurora beam.
If it's only out of those four, I'd go with Psychic, since I seem to always have at least one that uses it on the team. Same goes for Ice Beam. Both come in handy often.
Surf, because going out of the Pokemon world & into reality, a giant tsunami would cause more damage & repair than an Earthquake. (And A Psychic & Ice Beam?)