Now that I've seen the movie twice and let it stewed in my head for a couple of weeks now, the answer for me, at least, is Jack. Yes, I'm drawn to Ennis because of the tragic outcome of his story, but if I had to choose to be with one of them, I would definitely choose Jack.
I remember listening to the song, "I Don't Want to Say Goodbye", and while Jack was slow dancing with Lureen, there was one shot where there was a smile on face and in the next, he had an incredible sad and distant look in his eyes. Although he knew how to have fun, he still felt sad and empty inside because he will always love Ennis deeply.
The second song, "I will Never Let You Go", is a lot more fast past and cheery, but it also described Jack's feelings as he twirled on the dance floor with the foreman's wife. I believe the movie did a good job illustrating that although he was attracted to the Foreman himself, he will never let go of Ennis as the song suggests.
Although Jack never said, "I love you" directly to Ennis at any point in the movie, he has expressed his feelings more than once to him and that's something I appreciate about his character. I'm like that. I'm the type of guy who would devote the rest of my life loving the guy I fall in love with and I would wait for him like Jack would, even if I were to suffer through hell for it. All I want is to be with him as the lyrics of the first song goes, as simple as that. That's why it was hard for me to watch Jack's character, I could feel his pain as he waited for Ennis; I would have done the same just to be with the person I love.