Both are very fun. BM66 has very deep code, with a ton of risk and reward that keeps it fun and challenging.
The layout is a bit clunky, it is mostly just okay as far as the shots go. The code helps make up for it.

Deadpool has a great layout that is fun to shoot with very good rules. The code is reasonably deep, but not as deep and intricate as batman66.

Batman 66 offers a bit more variety of ways to play the game than Deadpool, but the Deadpool shots are more fun to shoot so its a bit of a toss up!

They both have pretty strong theme integration and great call outs so you can't go wrong with either there.

Deadpool is probably a better game to play multiplayer.

BM66 can be really long, so not super fun in multiplayer mode.