The Thompson fun is derived as much from the history as actually shooting it. Having the opportunity to shoot all the MP5s in that package and the Tommy Gun the MP5 (almost as iconic) is so accurate and easy to shoot the fun level is pretty much a tie. Something tells me an MP40 would be up there as well.
Admittedly I wasn't trying to punch one ragged hole in paper with either MG. I was ringing silhouette steel with them at 100 yards, and both were plenty accurate for that. (To be fair, the guns are both far more accurate than my old eyes are with iron sights. I didn't used to need the crutch of optics, but I'm no longer as young as I once was.)
Back on topic, I'd -love- to try all the MG's in that package!