In the 'big enough for service/duty, but still concealable' category, you've got the Glock 19, S&W M&P 2.0 Compact, and SIG P320 Compact as popular picks with police departments these days. There are others (Walther PPQs, H&K VP9, and CZ P-10C are very nice), but most won't have the parts/holster support of the SIG, Glock, and S&W. These pistols will be easier to shoot, but harder to conceal than the following categories. Oh, and if it's not significantly more, a Gen 5 Glock is superior to a Gen 4. Smoother trigger and more mechanically accurate.