MGR has better bosses gameplay wise, but DmC blows it out of the water in terms of overall boss awesomeness.
The music, the environment, the sheer size of the damn bosses. So ******* good. MGR puts you against the bosses with just the same type metal that you hear while fighting. The music for the bosses in DmC completely suits them. Heavy, dirty dubstep for ugly Poison, glitch/glitchstep for Bob Barbas' talking head, and aggressive DnB for the Hunter.
While I do think that the music fit the bosses in DmC, I'm really not a fan of dubstep or any kind of "step" music... Even DnB is kinda pushing it for me. Whereas I freaking LOVE metal, and I thought it was neat how the lyrics in the songs would only kick in when the boss was on its last legs in MGR.