Below you can find all my weapon rates for black ops 3 weapons.  Not used every weapon yet but based on the information here a rough list. Some tier 3 weapons are not bad but have nice niche.

Assault rifles

Tier 1: Man of war, M8A7

Tier 2: HVK, ICR-I

Tier 3: Sheiva

HVK is the best average gun in the game expect to see most people running it in public lobbies.

Sub machine gun

Tier 1: VMP, Pharo

Tier 2 Kuda, Vesper, Razorback

Tier 3 Weevil

Expect to see most players again using average guns Kuda, Razorback with some VMP.

Light machine guns

Tier 1 48 Dredge

Tier 2 BRM, Dingo

Tier 3 Gorgan

Expect to see most players running the BRM or Dingo

Shotguns

Tier 1

Tier 2 Haymaker, Argus

Tier 3 Brecci

Tier 4 KRM

KRM is just bad avoid it simple as that, wasted too much time on that gun trying to gold it given up.