I was stuck on act 5.4.6 Ultron for ages, and just couldn't seem to beat him with either loki or magneto. Someone on forums and reddit suggested that I use my top champ (human torch), and just power through ultron with the prefight. It worked! I finally finished act 5. Got this as a rewards, so pretty happy because she's one of my favourite champs to play:

What content should I do now? Start act 6, try and explore act 5 or a variant (I haven't done any). If variant, which one should I go for? Thanks to everyone on forums and reddit for helping me out!