Like anything else, it's a matter of opinion. Of the Sterns I've owned I would rank them:
1. Metallica (Pro)
2. LOTR
3. Spiderman
4. Kiss (Pro)
5. RBION
6. Sopranos
I'm an excellent example of a guy with collection ADD. I'm constantly buying/selling/trading, and doing so before getting very far into most of my games. With that said, Metallica is the only game that entered my collection that I thought "Something would have to go REALLY wrong in my life in order to sell this machine." The only other machine I feel that way about is TZ (regretted selling it the first time around). I had a blast with nearly all the Stern titles I've owned/own, but Metallica is by far the most enjoyable IMO. I wouldn't mind another LOTR down the road, but I don't NEED to own it the way I do Metallica. Spiderman will likely leave within the next few months. Again, great game, but not bolted to the floor the way Met is.