I’d steer away from full auto M4s. They’re very flat shooting and you see that platform everywhere. Go with either a pistol caliber or battle rifle caliber for real fun. It’ll have more recoil and blast. I hear the Tommy gun is a classic but isn’t very ergonomic and many would prefer shooting something else. I’d lean towards the MP5 if your only options are what’s in the picture. That said, if they’ve got an MP40, Swedish K (M45 I think), M3 grease gun, PPS43 or PPSH41, anything Suomi, Uzi (full size), VZ61 Skorpian, AKM, G3, FAL, M14, M60, M240, M249, MG42 or MG3, PKM, Bren (magazine on top), Lewis gun, DP27/DP28, or anything of that nature you’re bound to have a fun time. You can shoot 22LR for days without much cost of ammo, but I still think the loud boom and recoil is part of the fun full auto experience. And yes, the STEN gun is an option too, but it’s not as controllable, so you can’t go full blast like some of the others on the list as easily.