For me, like I'm guessing many of you, it's changed over the years and now depends mostly on the weather and how I'm dressed. Lately it's been a Colt Defender, .45acp, with 2 spare Wilson 7 round mags.
When it's colder usually a full size M&P 9 with 2 spare full capacity mags. The 3" 64 I just picked up will rotate in once the Lobo holster arrives for it.
All ride exactly in the same location and in similar holsters, for me it's a muscle memory thing.