I think that’s a question for the remainder of your roster to be honest. I only really play 4*s that are champed, so for me that is:
G4mora, Coulson, Rogue, Vulture, Nico, Nightcrawler, C&D, Hobofist, Mordo, Kingpin, Yondu, Chavez, C4rol, Lockjaw, Sandman, Main Event, Medusa, Mockingbird, 4ocket, Shuri, Hulkbuster, and Thing.
The ONLY team I see running Mr F is Carnage/Medusa in simulator (obviously PVP isn’t the end-all, but it’s the only place to go to see other folks’ teams), though I could see him adding value to a Shuri team. I know even less about who to put with Nova than that, though i do like him the times I’ve used him in his Crash/Burrito nodes or whatever. My Mr-F is 2/2/3 so I barely know what he even does.
I’m not sure my personal priorities are optimal, or reflective of the group though lol. For instance: I have 2 covers for Spider-Woman on the vine, and rather than try to save them I’ve chosen to champ 3 3s this weekend because I want to finish off that tier before going any further with my 4s (i have 6 3s left to champ now). My 2* farm is about to be down to just Bagman at champ so I need to start turning them back on. I have Peggy, Nova, Professor-X, and Spider-Woman waiting on iso, and I’ll probably champ them in that order as I get it. I do have quite a few more at 12 covers, and assuming 13ths will come in, that may affect my order of champing. I definitely want Peggy next though.
Hopefully that helps put my recommendations in context at least.