aah
usually, you compare one type of gun with the same type.
say:
>Handgun drops (or in a shop), I'm using (or switch) to my handgun.
>stats shown when looking at it will be compared to what you have equipped.
at this point, you compare damage - acc - reload speed - etc.
>main stat to compare would be Damage/Acc to your current one.
if this passes....
>Equip new gun and test fire it. Why?
a lot of weapons have gimmicks, so checking these gimmicks just to make sure these fit your playstyle or break it.
[burst fire, toss weapon like a grenade when reloading, extra melee dmg, etc.]
>if gun checks fine, keep and replace old one.
as the game progresses and start seeing new rarity Tiers...
White < Green < Blue < Purple < Orange
so if you have a blue Handgun, it would be pointless to even pickup a white handgun, and so forth.