"Star Trek is the first one of the 3 I came across and used to watch it a lot on VHS when I was a kid. It will always hold a special place.
Stargate is an awesome one in most respects (setting, story and character wise). Its also the only one that is a single movie and not the franchise (which means the movie has the beginig and the end :D ), though I read there are plans to make it a franchise with a sequels, reboots and whatnot.
As for the Star Wars, it somehow never grew up on me. I can watch it and its fine, but Im no fan of it.
As for the themed slots, I never played Gthech's Stargate so I would probably go with Microgaming's Star Trek :D"