Whatever you enjoy the most. Your Dark is probably the strongest of the bunch, but.Base Atk doesn't matter all that much, by far the most important thing is to have one team which has a Grid filled with slvl20 Assault weapons. If SSRs are not available from Epic quests and what you've farmed before, you should get SRs from Standard/Expert Disaster raids.
Find yourself a Union that can carry you Ults so that you can get an offensive Soul weapon, which should probably be Hercules' Axe.