...Heihachi and Hwoarang are forced, lolwut?
If you don't include Hei in this game, people would riot. Plus the roster seems to be built as much around people who would actually team together as just playability.
With that in mind, if Hei's gonna be in the game, which he damn well should be, Kuma makes the most sense to team with him. King is obviously an easy choice, Marduk's his best friend, easy add. Hwoarang is a very decent add. Brings a style not too often seen in these games and he's also well known enough for people to recognize him.
But since we're on the subject, what would be your Tekken cast at this point, while taking pairs into account?