My dream lineup for a game like this (because, it begs for it)
TF G1 was all about characters. Hearing these guys talking/reacting during battle is all you would need really.
BTW a few of these actors are no longer with us sadly, that's why this is a dream list
Optimus
Ironhide
Jazz
Ratchet
Perceptor or Blaster
Cliffjumper (Casey Kasem!!!)
Prowl
Starscream
Megs
Devastator
Soundwave & Rumble
Reflector ('cause he is a goddamned
camera)
Combaticons
Blitzwing (tank/plane/robot would just be too cool) or Astrotrain
Shockwave (Pussy cartoon version, or badass comic version)
End Boss Unicron! How the hell would they manage that I wonder..?