I'd like to suggest GOLEM for A Rank! (or at least B Rank)
seriously Golem was the MVP for me for Crawlis and Angies Gym!
three words: STURDY STEALTH ROCKS
No matter what the enemy does... well except multi-hit super effective moves... Golem will stand it's ground and it WILL get those stealth rocks out and absoluteley cripple the enemy team!
For now, we have: Crawli, Angie and Marianette (Swellow) that gets super crippled... and we will get more: Amber as the fire-leader (I assume), Flying-leader, Tesla (Fire-Elite 8 ... dat Talonflame will like instantly die...)
and it learns Earthquake as a bonus!
Golem is a pretty bulky physical attacker, which it's two main STAB moves EQ and Stone Edge happen to be, sadly it get's totally wrecked by any special water or grass move instantly due to it's low SP.Def and double weakness... but thats wat sturdy is for!
and Graveler is the boss against the Dimensional Rift Galvantula... they can do NOTHING about it while you prepare Rock Polish and stomp them with Rollout!