Choice Band Genesect is just dirty right now. Most often CB U-turn is a lose-lose situation for the opponent. If the opponent stays in, you will hit them for a huge chunk of damage. If they switch, you get a good amount of chip damage in and get a free switch to whatever you want. The switches it forces are more compelling for bulkier teams than the scarf set. You don't lose the ability to force a switch against offensive teams though to pull off a U-turn because of that sexy boosted Extreme Speed. That boosted Extremespeed is a good option for offensive teams to bypass Talonflame. Rotom-W is a great choice in this meta right now since it can check so many top threats and makes a great partner with Genesect to do VoltTurn. The pairing is obvious, but I really cannot express how much work they put in together to generate chip damage and free switchins for your team.
He makes one of the best partners for Dragon-types since he can switch into revenge killing ice moves and he can remove the checks for Dragons, Blaze Kick roasts Steel-types and Iron Head destroys Faries / Ttar / Blissey. His moveset doesn't look it receives anyway to hit the metagame hard, but it just hits the targets it needs well enough.