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 (Gen1), 19 (Gen2), 21SF (RTF2), 26, 39
Glock Armorer (AC), Glock Instructor (IW)
Glock Advanced Armorer (AA)
Remington 870 Police Magnum, Benelli M1 S90
Smith & Wesson 13-2, 16-3, 36, 66-3, 681-3, 3000