I'm not sure either phone is "winning" on paper. It seems like each phone has an equal number of potential drawbacks and benefits, but like I said in the post, it'll be hard to tell until we get our hands on both to test them.
Personally, I wouldn't buy either one, as I find both TouchWiz and HTC Sense to be incredibly cloying interfaces that mess up a lot of what makes Android so smooth and intuitive. If I had to pick just one of these, though, based on the specs, I'd go with the S6. I really, really appreciate a high-res screen, even on a small device. You're going to see more beyond-HD video content in the near future, and it never hurts to have a way to watch it.