My Haxorus.
In the first game, I didn't know what Haxorus' stats were like, so he had a few special moves there, which took up space for his physical moves.
Then, I realized my mistake, and made a monster. All I needed to beat any gym was to Dragon Dance at least once, and then Dragon Claw everything. And when Dragon Claw was replaced with Dual Chop, thus getting an extra 20 STAB for each hit, with each hit having a base of 40, meaning that the attack is already as powerful as Dragon Claw, with an extra 40 STAB bonus, meaning it's more powerful than Dragon Rush, and add a Super Effective hit to it makes that damage double to 240.
Sheesh.
And if, by some unholy chance that Haxorus faints, then all I would need is my Lilligant, who you likely already know the moveset of.