There's a lot of weapons in NMRIH and many players don't realize how different they are and how big of an impact this can have on survival. As a near 300 hour NMRIH player (ladies please) I'll be sharing my general opinion on every weapon in the game as well as trying to explain its best use if it has any.

Tier 5: Nearly useless melee
Fists: You start with these by default. Does awful damage although fists stumble zombies often and have almost infinite stamina.
Kitchen knife: Seems to have less reach than fists and takes 5+ hits to kill a walker. Just completely avoid this weapon.
Cleaver: Has short reach but does ok damage. Tbh this weapon is rather rare and just shouldn't be picked up unless you have no other option.
Barricade hammer: Similar to cleaver. The barricade function will save your life in a high runner situation but as a weapon this is poor.
Tier 4: Light melee
Hatchet: Short reach but kills walkers reliably in 2 hits.
Pipe wrench: Short reach, low damage. This is only tier two because it has great stamina.
Baseball bat: Ok reach, damage, and stamina. The baseball bat is just ok in my eyes.
E-Tool: The best low tier melee. Solid damage and stamina but lacking in reach. Can be folded to increase damage at the cost of even more reach.
Tier:3 Heavy melee
Pick axe: Very low stamina but usually kills in one hit. The worst heavy melee but not by much.
Sledge hammer: Very low stamina but it one hit kills.
FUBAR: Does more damage but uses more stamina than sledge. They are nearly the same.
Tier 2: Good melee
Spade: Nice reach and ok damage. Not a popular option but its a very usable melee weapon.
Fire axe: 2 hit walker kill but low stamina. Good but care must be taken to not run out of energy.
Lead pipe: 2 hit walker kill with plenty of room to leave between you and the zombie. Only downside is higher stamina costs.
Crowbar: Ok damage but the reach and stamina make it a top tier melee.
Tier 1: Godly melee
Machete: Amazing reach, damage, and stamina. You almost don't need a gun.
Chainsaw: Requires gas but can mow through crowds most guns couldn't clear. However the chainsaw and its fuel takes up your entire inventory so you can't carry much else.
Abrasive saw: Much more rare and slightly less powerful chainsaw. Still great at clearing hordes and with its smaller size you might be able to carry more.

Tier 3: Poor handguns
Flare gun: Holds a single shot and the flares explode and ignite zombies. You can get yourself killed easily with this gun and in general its more of a backup tool than a full time weapon.
Ruger MK.III: 10 shot .22 pistol. Takes 2 shots to kill and does almost no body damage. The only thing supporting this gun at all is that you can carry a lot of .22 and most players ignore .22.
Beretta M9: These things are everywhere like the toyota camry of guns. The glock is a much better 9mm pistol in all aspects but I'd be lying if I said most games I don't have an M9.
Tier 2: Ok handguns
Colt 1911: One hit headshot and good damage overall. Only downside is low mag capacity.
S&W 686: Generally a one hit kill no matter what. Fires slowly in ADS and only holds 6 rounds but every shot is a kill.
Tier 1: Good handguns
Glock: The glock is truly the best in the game. Simply having a mag size of 17 means that it can do more than any gun before needing a reload. I know this ones gonna be controversial but its by far the best option for killing as many zombies as fast as possible.

Shotguns
Beretta SV10: Only holds two shots but does crazy damage. The best use of 12 gauge but its low mag and slow reload can get you in trouble if you don't have backup.
Mossberg 500A: 5 shots and high damage. Pick this for walker heavy maps.
Remington 870: 8 shots and lesser damage. Pick this for runner heavy maps.
Winchester super X3: Only holds 5 shots but its also the only semi auto shotgun. Damage is poor so prepared to waste 12 gauge if you want to use this.
Tier 3: Poor rifles
Ruger 10/22: Only holding 10 shots and doing no damage this is a great gun for getting killed. The ruger pistol is smaller and has the same stats.
Sako 85: Holds 5 rounds and is bolt action. Although damage is very high it's not forgiving if you miss. Can have a scope if you want to try to snipe in this fog heavy game.
JAE-700: A purpose sniper. Holds 10 shots and has faster bolt speed than sako. If sniping's your calling this is the best sniper. It's still a poor weapon though.
Mac-10: It kills very well but it wastes 30 rounds in seconds. Just unload this gun and use the ammo in your 1911.
Winchester 1892: Holds a good 16 rounds and does high damage but being lever action gives it a slow enough rate of fire to cause trouble.
Tier 2: Ok rifles
Simonov SKS: Does good damage but only holding 10 rounds isn't enough. Can be had with a bayonet that is very risky to use.
Ruger 10/22 (extended mag): A 25 round mag changes this gun enough to move it up a tier. Stats are the same but 25 rounds lets it perform much better.
H&K MP5A3: This one can be argued but the mp5 lacks in damage. Even a 30 round 9mm is still a 9mm and it just doesn't kill as well as you want.
Tier 1: Good rifles
M16A4: 30 rounds and very accurate this is one of the best guns in the game. Only downside being that 5.56 can be very rare on some maps. Can also be had with an acog if you still think sniping works for you.
CZ858: Nearly identical to the m16a4. Does slightly higher damage and only comes with iron sights.
FN-FAL: Limited mag but 308 in semi auto makes you feel like zeus the way you smite everything in your path. Best gun in my opinion if you can keep it fed.

Grenade: Kinda sucks. Only kills zombies that are standing right on top of it but has a good stumble effect.
TNT: What you wish the grenade did. Will clear an entire room but be careful to not blow yourself up.
Molotov: Somehow the best explosive despite not being explosive. It creates a large patch of fire than will ignite any zombie in it. While burning zombies stay alive for a while if you just walk behind a wall a molotov can get you an ez 50 kills.