The ubiquitous .38 spl. S&W Model 10/15 for a one and one only revolver choice myself.
Or a S&W 17/18 in .22lr.
Either or any of the above would do me well if limited to an "Only One" choice.
Youth rebels, age conserves; between them, they advance. The Marines will cease to win battles the moment either camp achieves ascendancy. – Robert Leckie, Helmet for my Pillow