Glock 9mm as I could get the Lone Wolf G9 in the Ar with interchangeable mags. With so many options for the glock pistols, the added ability of LW G9 and the availability of 9mm ammo it make sense.
Some will tell you that the 9mm for SHTF is nuts. Well we are talking about one manufacturer, one caliber for multiple guns. Weight equals pain. I can carry tons of 9mm where 5.56, 7.62, 223 etc., you are limited by weight and room. The second thing is some will say you cant hunt with 9mm. Bull. I have taken deer with a 22 and the 9mm G9 will be sufficient for deer to small game. It's shot placement and when grew up, I used a single shot and you had to make sure your one shot was up close and counted.
I like the 9mm but own 22's, 300, 30-06, 45, 30-30, 12g, 410, Ar15, AK47, G9 several glocks, CZs, Bersa's, Berretta's and the odd wall hangers and a few collectors. If I could carry them all, I would carry them all, but if I had to choose I think I would have made the right choice.