Well, I know who I would prefer, if it was "who should Megan end up with?" but that's not the question here.
Don't put me in anyone's army just yet, but here are my thoughts.
I had a hard time deciding who Katniss would be better off with throughout the books. In the end, though, I think it was right for her to be with Peeta. She's obviously a bit off her rocker by that point, and permanently scarred in so many ways. The only person who can truly understand what she's going through is the one who was there with her through all the trauma.
With the war over and her mental state so fragile, Katniss needs peace and stability. Gale is too much of a mover and a doer to settle down and do nothing but try to make it through the day. He's a war hero with big ambitions and a sense of responsibility to the new country. He could never sit at home all day with Katniss, and I think that's what she needed in the end - someone to be nearby all the time, to comfort her through nightmares and panic attacks. I just think she was so delicate by the end, that she needed someone who treated her delicately. And that is Peeta.
And, frankly, I think Peeta deserved to end up with her. He loved her so much for so long, and was more than willing to give up everything for her. He cared about nothing
else. My heart was breaking for him the whole time. It seemed Gale would have an easier time moving on to someone else, or distracting himself with all his other activities.