Disagree on so many of these. Normally I'd make a tier list for a game like this immediately, but a major issue here is that the game forces you to use whatever you can get your hands on. Skills also vary in usefulness between guns. Adding ammo to the SMG makes it much better, but it doesn't do much for the low ammo weapons. There's also the temporary weapons or the weapons you really only find for boss fights that are really difficult to rate in comparison to the weapons you can replenish the ammo of, etc, etc.
Going to make a quick list now anyways, I'm basing this on memory and the gun range instead of live testing because I wasn't planning to do this (My assault rifle scores especially will be questionable since I always grab them and they're pretty similar.). Most of my experience with these weapons is using the reload+max ammo count perks (But not the increased headshot damage).
Battlehawk (4/5): Accuracy and ammo per clip is a bit low, keeping it from a better score, but it's still really useful.
CM2000 (4/5): One of the only restockable weapons that can kill the red boss zombies before they can even reach you. It's one of the best dps weapons if you're accurate enough to use it well. Even body shots are pretty lethal if you're lazy about aiming. Also great for farming headshots for more points and can even be used like a shotgun if you want.
SKS (1.5/5): Overall worse than the above two options. At the very least it's accurate and can be used as a poor man's CM2000 for headshot farming.
KA47 (2.5/5): Good burst damage and accuracy but it has a low clip size and poor uptime with it's longish reload time.
AR4 (2/5): The 3 round burst can feel annoying at first compared to the full auto weapons, but it actually has surprising damage and accuracy. What really hurts it is the small clip size, it runs through a clip way too fast to be useful against swarms.
SMG90 (3.5/5): It kills pretty slow but has a high clip count and max ammo. It benefits greatly from boosting your max ammo or using the talent for more headshot damage. Initially jerks to the top right a bit but calms down, so takes some practice to not miss the first shots.
AP5 (3/5): Pretty similar to the SMG90 with less ammo. It also jerks straight up so it's a bit more logical about recoil.
Vo14 (1.5/5): Low damage, low clip size. It's the only main hand weapon that has trouble killing a single mutant on hard mode with a full clip.
N90 (3/5): Much better than the Vo14 at least, it has a massive clip size that's great at dealing with swarms. Pretty low burst damage though and slow to kill mutants, but at least you won't be stuck reloading multiple times in a fight. You could skip the reload perk while using this and you wouldn't be punished too often for it since it has enough ammo to get through most fights with one clip + swapping to your secondary.
Moss500 (2/5): Low rate of fire and slowish reload speed. It still has good burst damage and beats out the total junk weapons, but all the other shotguns are clear overall improvements.
Shot12 (3/5): Overall improvement to Moss500.
MAS12 (4.5/5): Probably the best overall weapon in the game atm (that's restockable at ammo crate). The huge boost over the other shotguns is it reloads by clip rather than individual bullets, improving the uptime on its damage tremendously. It reloads twice as fast as the Moss500 with the level 2 reload perk (About 2 seconds vs 4 seconds).
Phantom (4/5): Might annoy you with it's thermal scope, but it has really high damage compared to the other smgs and even the assault rifles. The only thing that hurts it really is it runs through it's clip pretty fast and it's reload speed is on the slower end (About 3 seconds with reload perk), meaning it's uptime is a bit low.
GreLauncher (3.5/5): Difficult to rate because it's more of an offhand weapon you use for swarms. It becomes more useful later on when the enhanced normal zombies start appearing as well. It's wise to run around pulling a ton of mobs on you and wait for them to group up on you before firing, requiring much different tactics than you'd usually use.
Flamethrower (4.5/5): Really great, pick it up if you can afford to even with its poor range/ammo count. It can wipe out entire rooms of minibosses/bosses pretty quickly.
Pulse Rifle (4/5): The boss killing weapon. Less useful against mobs due to its windup, but handles any of the bosses/minibosses extremely well.
Chainsaw (4/5): Kills a bit faster than the flamethrower I think, but the poor range can make dealing with certain zombies difficult.
Katana (3/5): Can headshot pretty easily, but does have some dps issues against minibosses. Takes a bit more skill to use well than the chainsaw or flamethrower when it comes to temporary weapons, which hurts its score.
Denma (3.5/5): The special attack it uses actually does tremendous damage if you can land it. It's also more forgiving than the katana since you can just hold down the attack button and run into enemies.
Arc Sword (4/5): Really high damage, though you're unlikely to find this outside certain boss/mini boss fights. The special attack is really cool, though can be difficult to land on the agile enemies or when being mobbed.
Rocket Launcher (4/5): Again, mostly used for boss fights.
Cyber Pistol (1.5): I don't know how this is considered in the same tier as the revolver. Kind of feels like a semi auto Vo14. It does have a high fire rate and quick reload, but it's really not worth 2 talent slots (Pistol + Default Weapon Reload).
Revolver (3.5/5): Legit main hand weapon. If you put 2 talent points into this (Gun + Default Weapon Reload) instead of the main hand reload/ammo count perks, you'll have a reliable guaranteed weapon every map. 1-2 body shots to kill normal zombies, headshots like the sniper rifle. Can kill most mutants with a single clip. Also note: Not worth the extra clip size perk taking up a 3rd slot, it only adds 2 bullets. With how quickly it reloads, it's better used on something else most likely. It also has one of those "Large bullets" like the sniper rifle that means it can more easily get headshots than a lot of weapons.
I killed the final boss with the revolver only on hard in 5 minutes, with some point farming on the side mobs, lol. I'd use it more if it didn't kill my hand to click a million times.