Can’t really go wrong either way, easily the two best Spike games. Enjoyment may actually come down to your skill level. Maiden really comes to life once you’ve gotten a bit deep into the game.
If you can regularly put up a few hundred million on IM you probably have what it takes to dive deep into that and it would be a more satisfying game in the long term. If you’re a more casual player and don’t frequently get past the surface level on games I think Deadpool would be more satisfying. The shots all feel good and there are a lot of little payoffs along the way.
Deadpool is pure fun, Maiden is pure adrenaline, both kick ass.