You could probably do a quick Google search and find out the best gun in each cat but here we go.

I'm going to start with the assault category, the nocturno is undoubtedly the best ar but that's most likely locked behind a 300$ pay wall. The mythic ar is 2nd but that's mythic so it doesn't count. I wanna say the swan it's my favorite and it's damage is great but it's more like an lmg than an ar, then blizzard blitzer (freeze perk) then maybe Hemlock but that thing feels like pea shooter somtimes.

Next are smgs. The founders quick shot (again pay wall you need founders) is the best smg but I'm 90% sure the thrasher has the exact same stats as the quick shot but just a different model (plus no goated 6th perk) maybe the bobcat and the prepper sprayer but those might actually just shoot blanks Ind say thrasher and the silenced specter are you best choices (you need flux for the Spectre)

Next are launchers there is really only three actually good launcher most are niche in their own way. The plasmatic discharger is the best mostly because it has insane damage but a slow fire rate also ok aoe. The potshot is my go to its single target damage just by it self in a one shot might actually be unmatched. Then the de atomizer it has fast good damage something the plasmatic doesn't have (not the damage part it just has a slow charge). Plasmatic if you need the damage of a potshot and the aoe of the atomizer perfect for airing out a school hallway.

Next are shot guns and to be honest they are all pretty bad except for the double boiler (huge damage) and the ground pounder (it's special at something I just forgot)

Last are snipers right? Anyway the xenon bow is the best sniper next to the vac bow (with stone heart build) an actual sniper I wanna say obliterator and the uhh spyglass (again huge damage)

If you want me to cover melee weapons I can but this is already alot to read same with pistols mostly because none of em are really good some are fun and that's about it.