The 19 is a good goldilocks size, not tiny, but just a but under full size, still enough for me to get a full hand on the grip. It was one of my first firearms. I agree with one of the previous posters that for a beginner, it's really hard to know what feels good, or what a good trigger is, etc. Even going to the range and renting a bunch, they all just felt just fine to me. Obviously, larger, heavier, metal framed guns had less felt recoil, which was nice, but also was got tiring because of the weight.
I picked the 19 as I felt that I could resell it very easily if I wanted, and I liked the very simple take down process. I didn't resell it though, I still shoot it often and liked it enough to purchase several more Glocks. If I were starting over, I might have went with the 17. While the 19 is a great size, it's still not quite small enough for me to conceal comfortably, so at that point, as home and range gun, I might as well have gone with the bigger 17 since I'd end up with a smaller carry gun anyway.