If I could only own one handgun, it would be a boring old midsize 9mm auto-loader......something with a 3.7" to 4" barrel and a standard capacity of 12 to 15 rounds.

Pretty much every reputable manufacturer makes a model that fills that spec. And now-a-days many come with a dust cover rail and with the slide cut for an optic.....so you can run it "slick" or add a white light and/or red dot optic if needed....

....and most times you have the option of using extended mags with a higher capacity or even adding a threaded barrel to mount a suppressor/silencer.