I strongly promote settling on a “family” of guns as your primary defensive handgun option. Personally, I use the Glock 9mm family, in particular the Glock 19 and Glock 26. I don’t bother with the small-frame Glocks like the model 43 because they don’t accept the standard magazines. Being restricted to model specific single-stack magazines is my biggest turnoff regarding single stack models. I find that accommodating the slightly wider gun, such as the model 26, is completely worthwhile due to the enhanced capability the double-stack magazine provides. The flush fit 10 round magazine for the Glock 26 can easily be swapped for a 12, 15, 17, 21, or 33 round magazine. The versatility is amazing, thus the Glock 26 remains my primary carry gun. I can make it quite tiny, or I can load it up so that it gives up relatively little to a service-sized pistol.
I used to carry a Glock 19 most of the time and I still use one often, and the 19 is my preferred house gun. Obviously, a Glock 17 or 34 make wonderful house guns as well, as the larger size is only a plus rather than a negative if the gun is not a concealment piece. Such magazine compatibility makes this line of handgun exceedingly versatile. The Glock line, however, is not the only handgun family with such magazine compatibility. The Smith and Wesson M&P and the Sig P320 lines also work in this manner, as do many other handgun families. In my mind, the double-stack 9mm, in all of its size deviations, serves as the go-to self-defense tool of the contemporary age.