I wondered what that was. Thanks for pointing that out!
As for my favourite trio I haven't played with any enough to really determine that. I've played as Ace, Trey, Cater, Seven, Eight, Nine, Queen and Rem. Out of those three I'd say my favourites are Cater, Seven and Eight. Cater's charge feature is pretty good, Eight is just like POW POW POW and Seven's whip move (snakebite) packs a punch. I'm going to play more tonight and try out some more characters, and I haven't used the altocrystarium yet (which I've only just unlocked) so that might change once I unlock different abilities for my characters.