There’s two team formations that are easy to discuss: best character first, for OCV potential; and best character last, for comeback potential.
What about your second character? Let’s say, hypothetically, you play your first character until he/she is KO’d. Your second character comes in down one assist, and without max level X-Factor. Is that character at a disadvantage? Would you rather play your best character second to compensate this disadvantage, or would you rather still leave them for last? If you do leave them last, doesn’t that give the second character a better chance of being KO’d? Why not just play that character second so they have an assist and Level 2 X-Factor to win the match?
In my own experience, I’ve found that if my first character gets low on health, the thing to do is DHC him out of there. So now my second character is my point character. If I can safely DHC my first character out, why should I put my best character in first? If he gets his butt whupped I can just get him out of there, or if he gets KO’d, either way, my best character comes in and all is not lost. If anything, I want my first two characters to be interchangeable; they DHC and assist each other, and I have a particular knack for both of them.
Whether you just play the characters you like, or you play the characters you think are top tier, you still have to think about team format. I believe what will typify different teams in this game is how people decide their second character.