First impressions
Just handled my first Glocks today, actually. A 21 SF and a 30 SF. My hands are kind of between medium and large. Previously I've shot a 1911 and an HK-USP45C, both of which I liked. The Glocks really surprised me - I was expecting them to feel like a 2x4 at an odd angle, but to my hand both the 21 and the 30 fit really well. Very natural to me, so maybe I just have Glock hands. Anyway, the 21 is not small, but to me it felt like a smaller gun than it really is. Felt very well balanced. The 30 is not really that small and filled my hand very well. It might be a little on the thick side for CC for some people. The 30 is referred to as a subcompact, but it doesn't feel like one to me. Between the 21 and the 30, both were great, but I slightly preferred the balance of the 21.
A buddy of mine carries a 23 as his daily carry and likes it very much. I'd definitely consider one for CC, or a 19.
21 or 23 - don't think you could go wrong either way, but you might want to check out a 30 as well.