I really like the G3, especially the 14.4 inch barreled version with collapsible stock. The 10th Special Forces Group bought a number during the Cold War but they werr never issued, politics.... The two down sides were the muzzle blast with the short barrel and the 2nd generation collapsible stock with the reverse curve buttplate. I have several frineds in Germany with the civilian version sold as the "officer's model" and they are very accurate despite the short barrel.
We also had MG3's that I like alot but the MAG58 is more practical for troops that have to carry their weapons with it's slower cyclic.
The UZI is a 1950's design that is very reliable but cannot be compared the more modern design. FWIW: The CAR15 with either the 10.5 or the 11.5 inch barrels were classifed as SMGs.
I have not fired the STG 90 but have quite a bit of experience with the SIG 556 series. Great guns but too expensive.
The M16/M4 have been in service now for more than 50 years so the design is pretty solid. Although the gas pistol versions are cleaner I don't consider it worth the additional cost especially not for a civilian who can clean his rifle as often as required without risking life and limb.
The M14 is a pretty robust design but production was actually halted because of quality issues, not becasue the M16 was beigng adopt. Great explanation in the book The Great Rifle Controversy" by CLinton Ezell.
Interesting, thanks.
edi