Optimus is great for solo and special missions because he has a lot of team related traits. Starscream makes a great arena and raid fighter because most people have the Courage mastery. Starscream can continuously nullify this mastery for an unlimited amount once the opponent reaches below half HP. It probably make him the most overpowered PvP character in the game. I often save up his S3 and completely destroy bots tree times his rating.
Comments
i scream
STARSCREAM
(but actually prime is better, just that i prefer to use starscream lol)