Transformed was far more ambitious, which lead to it feeling less polished than the first game, but that doesn't mant the first is a better game. The first played it so safe by comparison, so of course there are less wonky moments. I think Sumo did a fantastic job given the concept of Transformed. Felt far more like a SEGA game than the first.
I think both had strong rosters. I loved Ryo, Opa Opa and Bonanza Bros in the first one, but I equally loved Vyse, Ages, Gilius, Joe, and NiGHTS. True, the sequel has some garbage characters like Meemee, but given Sumo put secondaries like Gum, Meemee, Reala and Pudding in as a bonus, I'm okay with their addition. I like Gum and Reala especially, and Pudding has a cool all-star move.
I think Transformed had better tracks for sure, and nearly every IP from the first game returned as either new tracks or returning tracks.
I prefer new remixed music over existing music. If I want to choose my music, I can do the custom soundtrack option on my XBOX.
I preferred the first game's all-star moves, but again I totally get why they had to do what they did. The first game's ASM's were difficult to implement online. Still, first game wins in this category.
Overall, Transformed for me!