I would definitely choose heels and I will tell you why. Back in Bulgaria I used to use mostly high heels, I probably had just one or two pairs of flats that I used for Sports at school. Even if I was wearing heels all the time, my legs were never tired:)
Now the situation changed a little bit. I do wear more flats than heels now-at work, at school. But the fact is that I still have more high heels than flats. When I go to the shoe shops my eyes can see only heels. Strange, right?