The most prominent weapons in tier S are Legendary Scar and Railgun; they are the most lethal weapons in the game. Kymera Ray Gun and Bolt Action Sniper are the best weapons; you can also pick them up.
Pulse Rifle and Burst Assault Rifle ranks in tier B. Some weapons in tier C are Assault Rifle and Rocket Launcher, while Pistol and Hand Cannon rank in tier D.
S Tier

Legendary Scar |
Rail Gun |
Rapid Fire SMG |
A Tier

Kymera Ray Gun |
Bolt Action Sniper |
Pump Shotgun |
Submachine Gun |
B Tier

Pulse Rifle |
Burst Assault Rifle |
Heavy Assault Rifle |
Tactical Shotgun |
C Tier

Assault Rifle |
Rocket Launcher |
Lever Action Shotgun |
D Tier

Pistol |
Hand Cannon |
Recon Scanner |