9mm is my agency-mandated caliber. The G26 is issued, and my lightly-customized G19 has (now) become my overall favorite Glock. The G37 would be MY choice of an ideal service sidearm (the 9mm-sized frame gives me optimal control of the .45 round, and I can't help but appreciate a gun purpose-built around a new caliber).
The G17 gets a most-honorable mention. It's hard to limit my selections to three!! I'm also anxious to try a Gen4 G37.
Glock 17, 19, 21SF, 26, 37, 39
Glock Advanced Armorer (AA), Glock Instructor Workshop (IW)
Remington 870, Benelli M1, Smith & Wesson 3000, Mossberg 500