Peeta for Katniss, obviously, I always go with what actually happens in the books (like harry/ hermione shippers? what?) and I personally would rather have Peeta as well.
I think people often confuse this question with "Who should Katniss have ended up with romantically?" which, to some, may have the same answer, but for me, they are entirely different. I prefer Gale because, throughout the course of the trilogy, he never loses sight of whats important to him, he never gives up on his ideals, and he doesn't get MIND FREAKED!!!!. You can't say the same for Peeta, or Katniss herself for that matter. Peeta consistently changes, both in the minds of the reader, and in the actual plot events. He is extremely dynamic, and by the end of the series, I was confused about whether or not I even still liked him. Certainly early on he was extremely admirable, and I definitely was in his corner, whereas you didn't see much of Gale at all, only a vague sense of a genuinely nice guy, but with no real plot support to back it up. By the end, however, we have seen just what kind of stable, honorable, and champion stuff Gale is made of, while Peeta (SPOILER ALERT) has had his poor mental and emotional capacity screwed with by Tracker Jacker venom. All in all, though, I still believed Peeta to be the one Katniss was destined to be with, from start to finish, just because of the intense romantic emotions she felt for him, and the fact that she couldn't explain them, whereas Gale always appears as more of a best friend, or brother.
Team Peeta! Gale is an amazing person but he's not right for Katniss, as she says with the whole "I had plenty of fire of my own. What I needed was the dandelion in the spring..." etc, etc. (sorry, I might have misquoted but I've only read Mockingjay once and I don't have my own copy). Plus technically, Peeta knew her before Gale did because he gave her the bread before Katniss and Gale's first encounter. :)
As i read the books i was always Peeta but when i saw the movie Gale seemed to be a bigger part of Katniss's life.
I never saw Gale as a bad person, I just always liked Peeta more. Gale has always struck me as an angry person. I loved the friendship between Katniss and Gale, but the romantic situations never felt right. Peeta loves Katniss for who she is. He sees through al of her flaws, and forgives her for hurting him time and time again. I choose Peeta.