I don't know how anyone can make that decision yet. You'd obviously want them to be your 5 best fighters, since you'll have to fight for squares. How could you possibly know who those 5 are already.
In Deadly Alliance, Nitara and Frost ended up being my best characters. I didn't know they would be before I got it. So I have no idea now. I personally think Hotaru looks like a pud, but I could end up rocking with him for all I know, so he may end up being my head piece.
These are all decisions I will have to make later. After the game has been released.