[swaghauler]

This has already been said but I'll say it again. The 3 most common weapon types (according to BATF stats anyway) are:
1) The .22 LR Rimfire, with there being a virtually even mix of Semi, Pump, Lever, and Bolt guns.
2) The 12 gauge Shotgun, with the pump outnumbering Semi, Double, and bolt guns by at least 4 to 1. In a twist of irony; The Pump only outnumbers the Single Barrel by 2 to 1 (probably due to cost). The most common manufacturers are neck in neck for sales. Mossberg and Remington top the list with their Model 500 and model 870 pumps. The 20 gauge also had a strong showing. The .410 came in last and was primarily bolt or single barreled (mostly for small game).
3) The Larger Caliber hunting rifle, with four primary calibers outselling almost all others. The first (to my surprise) is the .30-30 with the lever action configuration being the most numerous (probably because it's been around for more than 100 years by the war). The second most popular caliber is 3006 with most rifles being bolt action (with a few semi, and pump actions thrown in). Round number three is the .308 Winchester/7.62mm N also primarily in bolt gun configuration. The last round that edged out the others (slightly but still surprisingly) was the .270 in bolt action. The .223 came in 6th in sales (behind the 8mm Mauser, another surprise). I didn't think the list by ammo would look quite like this.

Pistols were no surprise. The most commonly sold calibers were:
.22 LR Rimfire, with there being an almost equal number of Semis, and revolvers.
.38 Special, with the volume of guns being Revolvers
9mm Parabellum, with the majority of guns being Autoloaders.
an almost equal number of users chose either the .40 S&W (a common LE loading) or the .45 ACP in Autoloading configuration.
Darkhorse candidates were; The .380 (Autoloader), The .357 Magnum (Revolver), The .44 Magnum (Revolver), and The .25 ACP (with a slight edge to Autoloaders).
The magazine capacity of magazines would be limited to 10 rounds IF The 94' Assault Weapons Ban is in effect in your world.

The most common "military arms" during this period would have been:
This makes the assumption that the 94' Assault Weapons Ban had passed.

AR-15 and the Mini-14; The AR-15 was severely restricted compared to the Mini-14. Mags would be limited to 10 rounds.
M-14s;these would be available but rare, as they were banned in 94' too. Mags would be restricted to 10 rounds.
M1 Garands; would be more common than the M14 because they were not banned.
M1 Carbines; Would be common as they were not banned. Mags would be limited to 10 rounds during the ban.
AK-47s; would have "thumbhole Sporter" stocks (mandated by "President Clinton" in 93') and would be about twice as numerous as ARs but only about as common as Mini-14s as they were completely restricted by the ban.
SKS Carbines;Surprisingly, these would be as common as AR-15s in America. Although they were banned in 94' as well; Norinco imported more than 10 Million of these before the ban (which is why you see them in the hands of all the "Militias" that formed in response to the ban). They were selling for as little as $100 US in 1990. A common modification was the replacement of the internal magazine with a "duckbilled" 30 round polymer magazine (pioneered by TAPCO) that could be had for $20 US. TAPCO made 2 million of these right before the ban took effect and replacement required only the disassembly of the rifle to remove the internal mag. The weapon could be easily converted back if the need presented itself.
FAL; These battle rifles would be about as common as M-14s. The more popular of the two types in America would be the "Inch Models" built on receivers from England. These outnumbered the "Metrics" at least 2 to 1. The "Inch Models" were more heavily built than the "Metrics" which was believed to promote accuracy. During the ban, "Inch Models" developed almost a cult following with enthusiasts.
SVD/Druganov; A small number of Russian guns and a fair number of Chinese Norinco guns did come into the country but were banned in 94'. They would be here but rare. Chinese guns would outnumber Russian guns 10 to 1 (which is why Russian guns command prices between $6K to $8K today).

There are other models, of course, but these are the most commonly encountered in the 90's (I know because I started my now 200 gun collection in 1991). After the ban was lifted in 2004; There was a veritable "explosion" of assault weapon production. ARs are probably the most common rifle now (but one's choice of weapons is almost overwhelming now).

Finally; A note about 12 gauge "Assault Weapons." The Atchissen Assault 12, The PANCOR Jackhammer, The Remington Streetsweeper, and a host of other "Combat Shotguns" using detachable magazines or high capacity drums were labeled "Destructive Devices" by "President Clinton" through Executive Order and either confiscated or registered as such. Therefore; such weapons will be rare in the US during this time frame.