if you have 5 Blue in Daken, Wolverine is definitely better with 5 Green, since you can setup an easy, efficient blast from Chemical Reaction from just one Feral Claws (+ the Strike Tiles from Daken) normally. He’s arguably better with 5 Green anyways, since his heal is more than enough at 3 covers for most of your matches you’re going to use them on (i.e. matches on your level or lower).
Honestly, 2* Captian America just scales poorly. Most people don’t use him, though he has some merit for PvE, I suppose. I wouldn’t put any ISO-8 into him.
Human Torch is mid-tier imo. I maxed his Black and his Red for less conflict with Ares/Thor/Wolerine (because I consider his Green much worse than theirs and his Red is about on Par with Wolverine/Thor and better than Ares’ in most cases). He works really well with Daken, since Daken can cover Black for him, and then just True Heal the damage away. He works well with oBW also, since she can tank Black for him as well as steal extra AP with Espionage - as well, she can steal green/red AP with Recon.
Magneto is arguably the best 2* character, because of how strong he is with Storm (and to a lesser extent; Hawkeye). Maxing Purple is non-negotiable. I had Blue maxed for quite awhile, because I thought Wolverine’s Red was better and the board shake was nice (and my Storm was poorly covered), but as my 2* roster has increased, I have switched over to maxing Red.
Ares is pretty much a mainstay. His Green and Yellow are just full of pain 
and he’s got tons of HP. I like to play him with oBW or Daken for color coverage and sustainability.
Captain Marvel seems pretty good. I don’t have her covered or leveled, so I can say much. She should play well with Daken/Wolverine because of her Black double dipping on their strike tiles. She should work well with Hawkeye because of her Yellow. She’s nothing to write home about herself, though, she basically fills in holes.
Storm is arguably the second best 2* - with Magneto and some boosts, you can easily tear down some 3* teams. Max Blue is non-negotiable. I’ve played some with max Yellow, and it’s good for some funny defensive wins, but overall, max Green is definitely better. The board shake and AP are just suburb for a 2*.
Thor is Thor. He’s got a lot of oomph and his two abilities feed into his Green. Not much to say about him though. I usually play him with oBW/Daken.
I played Daken 5/5/3 for awhile. I’m running 4/4/5 now and I’m not looking back. The increase in damage on Blue is amazing, and you won’t even notice the difference in the other two.
Hawkeye is a great, but he’s not good enough to be a priority. That being said, my go to team for difficult nodes is Hawkeye/Magneto/Storm - with Blue/Purple AP Boosts, +3 All AP Boosts, and Crit Damage Boosts it’s just wow. One Purple match and the game is practically over. The Catch-22 is, of course, that Hawkeye is completely an extra in this - he just makes the combo faster and more efficient.
Moonstone is someone I used to use - her Purple is pretty good and while her Black is expensive, is can be nice (like to steal an X-Force Healing Tile!
). That being said, she kind of falls into the 2* Captain America boat; her power scales very poorly compared to other champions. Can’t suggest putting ISO-8 into her.
Bullseye is kind of cute, I played around with him for awhile (I even regrettably maxed him
) but no. Keep him if you enjoy playing him, but he’s not good as he is.
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tl;dr verson; I would aim for the following: Ares and/or Thor as a bruiser. oBW for utility. Mags/Storm for mutilating synergy. Wolverine/Daken for sustainability. Hawkeye and Torch are good, but not mandatory. Moonstone, Bullseye, and Captain America are not worth an ISO-8 investment in the long haul. Save your ISO-8 until you have enough covers in someone to use them effectively, or level your useful guys (a.k.a. everyone but Moonstone, Bullseye, and Captain America) evenly.