Compact (Ruger SR9c) most of the time. Otherwise, duty size.
In my experience, most people carry subcompacts. I'm basing this on about 5 months behind the counter at a shop, combined with being the guy people tell everything to. I believe that people generally carry smaller than they have to.
Currently Own: Beretta PX4 9mm, Glock 23 (Gen 4), Glock 19 (Gen 4) x2