Well, that entirely depends on your group, and on what books you have available.
I suggest a genre that is not combat only: gurps shines in mysteries, chases, and social conniving. You do want to show some of it though: because Gurps has some awesome combat complexity.
If you have the books for them, Monster Hunters and Action both do this well: They support both combat and non-combat play, and they're pre-built genres that make character generation easier. I will admit though most of the time I play action I've mixed it in with a different genre-- with awesome results.
If you want monster hunters,
here is an idea thread. Some of them are adventures, some are campaigns.
Speaking of
Idea threads, we have one in the general roleplaying board.
I don't know that I'd suggest ISWAT for a starting campaign: It can be tricky for people to get their head around what they should build when they can build anything. On the other hand, I had lots of fun GMing an all mundane special forces team in infinite worlds trying to retrieve a captured conveyor from a Lich. That was a one shot, though I could have stretched the plot out to be a small campaign. I used Action templates.
But it all really depends on what sort of game you want to run, and what kind of players you have. So tell me what they enjoy, and we can give you better info.