a toss up between nova and deadpool my opinion. DP is a beast when boosted (strong red that true heals, high damage purple, and passive damage black) and pairs well with a champ xforce wolverine. Nova is cheap on powers and throws down mean strike tiles.
I don’t have a champ War Machine or Spider Gwen so I can’t help you there. Punisher MAX is awesome though. I would champ him first. Mordo is still in tokens at a higher rate, I believe, and he’s decent too. But definitely Punisher Max out of the two.
Second person, I don’t have Ghost Rider champed. I do have Nova and Xforce Deadpool champed. I really enjoy playing with both. I don’t think you can go wrong with either, so choose based on your favorite + how well they’ll fit in with the other people you’d use based on their colors.
Person #2: Nova! I have all three of those champed. Ghost Rider is fun, but most matches are over before he gets rolling (at which point he’s devastating.) X-Force Deadpool is slow but solid when boosted, he’s useful for climbing because he has a true heal, and his X-Enforcer is amazing whenever you’re in matches in which you’re guaranteed to take frequent powerful damage. For example, a PvP match against 4* Rocket and Groot, 4* Gamora, and Medusa. Even with all of her healing, you can take out Medusa in a couple of turns with X-Enforcer as all of R&G’s strike tiles coupled with Medusa’s countdown and/or attack tile damage will be putting out two or three X-Enforcer countdowns a turn.
That said, Nova is good and fast so he has more day-to-day utility.
Brigadierbleu: As others have said, Nova uses his powers at a faster rate but Deadpool has true heal & a strong nuke all in one color. I give Nova a slight edge b/c he can send characters airborne. This move comes in most handy when CD tiles are set to expire or the other team is ready to fire off one of its powers. Both are worth champing, though!