I guess this thought has been at the back of my mind for a while, I just hadn't voiced it.
I recommend a number of different types of ammo for carry because 1) supply levels vary and 2) most modern defensive handgun loads from major manufacturers are really quite good and compare pretty well with one another. Segue to pretty photos...
Yesterday I shot some HST in .40 and .45 underwater. The photos are pretty cool.
I'm totally not done with this, by the way.
As pretty as this stuff is to look at, it is also painful - I have plenty of scars from being sliced and poked by metal objects, but holding those bullets in my hand almost made me shiver. I would definitely not want to get shot by any of that stuff (duh).
Really, though, I would not want to get shot by any of the modern hollowpoint designs (duh). Although there's a sort of evil beauty in an expanded HST, I don't think they'd give me any more of an edge over a "less pretty" bullet that performed in a similar manner. And so, while I do carry with HST most of the time, that's mostly because I've found HST easier than other types of quality handgun ammo. I also have mags loaded with Winchester Ranger T and Federal Tactical Bonded and Speer Gold Dot. My J frame is loaded with Federal Gold Medal Match wadcutters.
Yes, there are minor differences when it comes to penetration and expansion and performance through some barriers. The details truly do not concern me. I don't feel any safer with one type over another. They all function in my handguns. They all shoot decently well in terms of accuracy and precision. By the way, I use projectile weights on the medium to heavy end of the scale for a given caliber - 124 and 147 for 9mm, 165 and 180 for .40, and 230gr for .45.
There are two main things to look for when it comes to defensive ammo, and they're exactly the same as what to look for in hunting ammo - projectile design/construction and sectional density. Assuming that the projectile is impacting the target within its designed performance window, and that it is impacting in the right spot, little else matters. All of the modern hollowpoint designs have good construction, and heavier bullets for a given caliber mean higher sectional densities.
So stop freaking out about carry ammo. There are many things that will matter more in a self defense shooting than whether you were carrying P9HST3 or P40HST. Buy a lot of whatever you can find, make sure it works in your gun, and don't let it sit in mags too long (say, don't go past six months).
Have a nice day.