Valmets are indeed nice. Some of the models have a peep sight, which fixes my major beef with the AKs -- poor sights. If I have an AK and you're at 200 yards, you're not in all that much danger
. If I've got a Valmet, you'd best keep moving
. I don't like the push-in-and-rotate design for securing mags. More fumbly and takes longer than the M16 push-it-straight-in design.
Galils are supposed to be nice, but overly heavy. IIRC, they have an AK-like action so I would assume them to be reliable.
FALs are reliable in semi-auto. I've heard they tend to jam in full-auto, but don't have any first-hand experience. They're also overly heavy and the receiver is overly long, putting your support arm way, way out there when trying to shoot off-hand (I'm 5' 9" and wear 32" sleeves, so I'm not a midget). Sights on the FAL are only so-so and trigger isn't great. FALs also have the push-in-and-rotate design for securing mags.
The G3 is reliable. Fine when fired in semi-auto. Good for strafing the sky when firing full-auto (at least, in my hands).
But both the FAL and G3 are more accurately called battle rifles than assault rifles, as they fire full power 30 caliber ammunition (7.62Nato). Assault rifles use a reduced power cartridge (e.g., 5.56Nato or 7.62x39). Can't really compare assault rifles to battle rifles.
AUGs, like all bullpups, have a shorter overall length while retaining a long barrel for good ballistics. Problem is that they can't be fired from the off shoulder -- you'll catch the brass right in your face. Better not come up against any left-handed barricades and hope you're not the poor sucker assigned to patrol on the right side of the street. One problem with the AUG is that the "trigger guard" actually goes from the receiver down to the base of the pistol grip. All of your fingers fit inside the trigger guard. As a result, there isn't much protection for the trigger. I exchanged e-mail with an officer in the Australian army who said that they had suffered a number of negligent discharges with the AUG, far more than when they had FALs. He attributed it to the design of the trigger guard.
I like the M16. It has been shown to be quite flexible, available in M16 or M4 or M203 variants. I haven't had a problem with my AR15s, but there's the constant debate about whether or not M16s are reliable in the field. The stock trigger on most AR15s and M16s is pretty crummy. If you're getting a semi-auto AR15, there are lots of good 2-stage triggers that can fix that right up. The ergonomics of the M16 work quite well for me, and the sights are good. For a civilian who is unlikely to be dragging his rifle through the mud, or firing 1000 rounds in a firefight, I don't think the requirement to keep an AR15 reasonably clean is much of a drawback. And in the US, there's tons of spare parts and other cool stuff available for the AR15. So I think the AR15 is pretty hard to beat as a choice for a US civilian.
I'm currently drooling over the M96 Expeditionary Rifle, but haven't had a chance to handle or shoot one yet. They do sound as though they are a tad heavy, though.
I've hard the SIG 550 is quite a nice piece, but haven't had a chance to see or shoot one. They're quite rare and thus spendy
.
M1911