Cap i love Deadpool also,the funniest table i`ve played !!!Rome from the Core Collection pack. While it has its unbalanced scoring (82 million Romulus Jackpot? Really?), the machine also has a ton of atmosphere and gimmicks. Plus the music is epic.
On a more controversial note, Deadpool. Apparently there's a ton of people who hate this table despite being fans of the character. In my opinion, however, it's easily one of the best tables in the game. Deadpool's dialogue feels ripped out of the comics, the modes are really creative, and the stackable multiballs are a ton of fun to activate. I bet it's the center ramp that turns people off.
As for most underrated I have to go with Super League Football, there are some really inspired mechanics on that table and every single shot feels good to hit, it's probably the best table to score chase on (assuming you have a lot of free time- balls stay alive a bit too long on that one)
Also honorable mention to Venom, which is one of Zen's coolest tables but came and went pretty quietly