Glock 9mm with the following minor mods works just fine for me:
- Steel night sights
- Grip cavity plug
- Optional smooth trigger
- Optional extended slide release (old habits die hard)
Super reliable, low recoil, low muzzle-flip, highly corrosion-resistant, same trigger pull for every shot, shoots flat for easier long-range hits (if ya got the skillz), FMJ 9mm penetrates better than most calibers to overcome the ever-more-common lightweight body armor, plenty of shots on-tap, no futzing with moving manual safeties on and off (point-N-pull when you need it, finger off trigger and reholster when you don't), no decocking, easy to strip and maintain in the field.
For the ultimate in extreme longevity (as in, "able to be passed down to the next two generations"), add a titanium frame and replace all small/internal plastic parts with metal ones.