it kinda depends on weapon,but he are some tips for them

pistol:its probably better if you get faster recharge on grenade,and get higher attack speed and damage.

shotgun: Its probably best if you get attack speed and faster recharge speed and damage,mostly use your right click to dash and attack,and when you are right next to the enemy and aim at them it does damage

machine gun: Its probably best if you get faster recharge on right click and get more damage,but if you cant you should get more damage

the carver: Its probably best to get better dash, faster attack speed and more damage, just saying his super spawns rats and they can tank a hit and also the upgrades work on them too