Keep in mind the Glock was designed around the 9mm Parabellum cartridge. When you buy a Glock in 9mm you're buying the gun in the chambering it was designed for and it has been tested with the most.
But the fact that cops use one over the other isn't really an argument of the effectiveness or reliability of a cartridge.
One of the Sheriff's departments near me issues Glocks in .357 Sig to all their deputies. I know for a fact they've had a **** ton of malfunctions shooting hollow points in those guns on the range. But they keep right the **** on issuing them. 'Cause money and resistance to change.
Ok so my always humble opinion is this: the caliber of the weapon is more important so you want a .22, a 9mm, 12 gauge and either 5.56 or 7.62 as these are some of the most common ammo around (in the case of the .22 the most common)
.22 rifle would be the ruger 10/22 as its reliable, common and the ammo is cheap and you can use it on small game (and large game if you're a good shot) and to teach others who've never shot before
9mm pistol would go for whatever is most common in your area, glock probably
12 guage pump-action shot gun for reliability, 'nuff said
5.56 or 7.62 either the remington 700 as its one of the most accurate rifles "straight out of the box" or if you want something in semi or auto try the AK47 or L1A1 SLR (SLR is more accurate)