If you’re focusing on PvE, level the boosted characters. It will help you complete missions faster and easier. Cap is really crazy right now in the current event and you’ll build lots of ISO just by playing. You should also level OBW for healing and AP stealing if you want to minimize health pack use. If you have any other characters that are respectable in damage and covers colors Cap doesn’t, you should use them as well. Also, Wolverine is still pretty good right now until his balance patch hits. Nobody has a date one that yet.