I like both. They're both so different. ItI don't see why you can't like both. I mean in theory if you're asking for an absolute favorite, then yes you would have to narrow it down to one, but if you're just asking if someone likes something, you can definitely highly enjoy playing them both.
Also an RPG can have "new stuff" and "varied environments" and you can play a FPS with "progression" and "fully exploring things." You can also spend one or two hours or more in just one room in a FPS. Try playing a FPS like Mass Effect or Halo on the hardest difficulty.
People are getting so offended by the TC saying you can't say both when I'm pretty sure he isn't some FPS fanboi like "NO RPGS SUCK, SO CHOOSE ONE". TC wants to know what you prefer. I'll be honest and say I like both, but I PREFER RPGs or shooters with RPG elements. My favorite FF is also 8. Though I don't think I played much of 9 and I definitely like the look of it.
I mean I like Mass Effect 2 and 3, 1 was good as well because it was more an RPG with shooter elements than a shooter with RPG elements. Yes I know Mass Effect is third person, but just pointing out that a lot of shooters I like usually have some amount of RPG elements to them.
Though I do like normal shooters too, BF3 is my favourite shooter, but I even have and enjoy a bit of CoD: Blops 2 every now and then.
I used to be a fan of FPS but I found I really don't like that type of game anymore. I think it would be awesome if Gearbox did a TPS version of Borderlands. But not call it Borderlands that way purists are still happy.