Hmm, I can't exactly decide here. Breloom is awesome, a kickboxing shroom that can put enemies to sleep then punch them to bits, but Heracross is good too and can be a Subreversal, or an Endurereversal and wreck teams if they don't have a Tyranitar. (He should be in the poll, I might've voted for Heracross if Heracross was in the poll) Medicham is also nice with beastly attack, but not that much defense but can destroy if it's a choice bander with Ninjask's speed boosts and maybe some extra attack baton passed to it.
But, I'll have to go with Breloom. Breloom can Focus Punch, spore, sky uppercut, and has other great moves to beat up stuff with.