I owned JM and re-watched the movie after 15 or so years and it helped make sense of the pin callouts and such. Great bang for the buck pinball.
Avatar I own... loved the movie and the pin makes excellent use of the theme and soundtrack, sounds, and callouts are excellent.
Ironman I haven't had tons of time with, but from what I have played I really like the pin quit alot.
I've also had limited time with Transformers, but from the 20 or so games I have played on one I liked it probably equal to or better than Ironman IMO.