I have a Glock 17 (full-sized 9mm) and will probably pick up a G26 (subcompact 9mm) soon.

I take it to the range at least once a month and shoot through a box of 100 each time. I bring my Ruger Mark II to fill out the rest of my hour of range time.

I chose the 9mm because it is the cheapest "serious" semi-auto caliber to shoot. I have it handy for self-defense because I am the most practiced with it.