You can not cause any damage to the enemy by hitting a grenade a couple of centimeters away from him.
Or you can kill few squads for shot
Admit it, you just wanted to show how good your shot was.
Of course
They are the best infantry weapon imo. Lends themselves well to large clumps of people like often seen in this game, and extremely annoying to have firefights with (indirect lololol). I think it’s okay since they’re limited to riflemen though, not much other reason to use those.
SF rifles and top MG and SMG are better.
SMG isn’t on my top list, it’s good up close but loses to bolt actions that react faster, and most LMG’s are just plain better for the same task. (first shot kills up close)
At range they range from meh to awful.
MG gets more kills than noob tube, but grenade rifles allow me to kill better players easily, by avoiding LOS and just exploding their general location. lol. Against people that are worse I can just shoot them normally, and the top end performance of LMG is unnecessary.
So I guess it depends if by “best” you mean “highest winrate” or “best score” 
Well, I evaluated the weapon as a simple player who has no problems shooting someone “1 vs 1”.
In any case, flamethrowers and rifles with a grenade launcher, as well as other weapons operating on the area are extremely good with a bad PC.
Well, in 1v1 scenario nade rifle is better. Needs less aim, doesn’t need los, just shoot at the ground the moment you see a rifle sticking out somewhere

