AK47 and Phoenix 350L are the best weapons in the S+ tier; these are the most lethal weapons in Back 4 Blood. The most prominent weapons in the S tier are Scar and Uzi; you can equip them along with your primary weapons.
M4 Carbine and MP5 are the best weapons in tier A, while AA12 and M16 are the best weapons in the B tier. The most prominent weapons in tier C are Ranch Rifle and 870 Express, which are just average weapons. 357 Magnum and Beretta M9 (Auto) are the best weapons in tier D.
S+ Tier

AK47 |
Phoenix 350L |
S Tier

Scar |
Uzi |
Glock 23 (Auto) |
TEC 9 |
A Tier

M4 Carbine |
MP5 |
Glock 23 |
UMP45 |
Vector |
Super 90 |
RPK |
Desert Eagle |
TAC14 |
M249 |
B Tier

AA12 |
M16 |
M1A |
Barrett M95 (Burst) |
C Tier

Ranch Rifle |
870 Express |
Barrett M95 |
The Belgian |
Fire Axe |
Hatchet |
D Tier

357 Magnum |
Beretta M9 (Auto) |
M1911 |
Bat |
Knife |
Machete |