Do the legal attacks against emulators and smaller developers count?
...serious now: Surf, Thunderbolt, Flamethrower, Ice Beam. For simple attacks it's the strongest that you can get without sacrificing accuracy. Surf in special, for being an HM that doesn't suck - because I don't bloody want to have a party of Bidoofs dammit. (I'm OK with having two Tropius though - one to fight, another to help.)
Metronome. The chaos of not knowing what attack is gonna happen is great.
It's why for a fan game I'm still in the planning phases of I plan on having a better version of metronome (name still undecided) that adds all attacking moves, but removes OHKO moves like sheer cold and removes all non-attacking moves. I have plans on making a special option in the intro to make every single pokemon only know this 30PP move.
the first Pokemon game i owned was XD on the GameCube, and like any good kid i overtrained my starter and ignored the rest of my team. i evolved Eevee into Flareon and Fire Blast quickly became my favorite move, killing anything and everything in just one shot. it only has 5 PP, though, so things started getting tough once trainers had six Pokemon. i eventually reached the Ground-type boss and never did get farther than that lmao. but my soft spot for Fire Blast still remains!
Dig, but I have a soft spot for Fortify because of its digital reticle animation and the hilarity of exposing you to tons of Metapod spamming it in the early stages of the game.