Avengers sequel is the best bet. The whole point of the other Marvel movies is to lead up to the next Avengers movie so I doubt one of them would be better than Avengers. I didn't really care for Man of Steel and with all things considered, I don't really have high hopes for the sequel. I know next to nothing about TMNT but I'm just expecting an explosion-fest/Megan Fox-fest. TMNT will probably be the worst.