Best type of characters for Speed Primary/Secondary mods at level 77

It really all depends on your lineup who should have priority, just keep your best speed mods on your arena team. If you're running rex, you want him fast to give TM on the opening move. If you have sith assassin, same idea, give tm on opening move. DN also does well with great speed to get his special off quicker. After the TM gain guys, I'd say attackers. if you're running DN Dooku, you could put offense mods on dooku instead of speed if you don't have enough to go around. He's mostly there for his counters.