I agree with the AR sentiment. If this is a "if I can only have 1" gun, then you want it to be something pretty universal. Meaning easy to fix/get parts for. A battle-proven platform with decades of modern success is hard to ignore. I'd go with an AR-10 set up to your personal liking.
I have a Bersa Thunder .45 UltraCompact (3.5" barrel), but they make one with a 4.3" barrel too if that's a selling point for you. I have had mine for 8+ years, daily carry. I have really come to love it (8 years will make you love or hate any gun, I'm sure). It's never had any problems with...
+1 for 500 guns. Have purchased two handguns from there and have been happy both times. Have also just looked around a few times and learned from the store keepers, they are helpful.
Great Point about the load. Also, being a revolver, frangables, large mouth hollows, and just about any other round should not give you any functionality issues, just differences in trajectory, etc. So options all around for you.
This is the first I've seen it, but it does seem to have similar DNA to the Bersas, not sure if that's just coincidence or not. Looks very interesting with the rotating barrel.
I have a Thunder .380 and a Thunder .45. Both are phenomenal guns in my oppinion. Not the smallest ever, but not bad. What I love is the balance, reliability, and accuracy. Of course most of this come with practice more than purchase.
I'm sure the Colt is great too, but I've never owned one.