Its not about which is more realistic or not, or which is easier to use or not, its about which makes gameplay more balanced and fun to play on a public server and competitive in a match.
So if you think about it that way, its obvious the impact grenades are the better choice. I understand what people say about just being able to throw a grenade against he wall and take out 4 people without needing to aim... but you gotta understand that that only happens if you are playing a super poor small map or the players suck and all jumble together, so thats not even a serious issue.
Whereas non-impact grendes can be just luck. Someone can just pick up a grenade, randomly toss it in the general area of the other team, and then run and pick up another grenade and randomly toss it in the general area of the other team again. Someone from the other team could turn a corner and then get hit by a random grenade. Theres absolutely no skill or strategy at all in that. So what happens is you get grenade tossing spray, so to speak.
Maybe if you could prime it before tossing it or something. The longer you hold the grenade before tossing it, the longer it will last before exploding. Otherwise you could just toss it righta way and it will explode on impact.
Or you could just make them however it was during the beta days, cuz then not as many people will complain.... Most people cant handle innovation