We have a guide on which grenades in Battlefield 4 are useful and which ones aren’t worth the inventory space. Get a quick study on what situations grenades are used on best. You can watch the video below, but we've also provided a text summary for your convenience.
In general, not all grenades are made the same. Many grenades aren't even worth carrying because of the limited use. You really only need a select number of grenade types for most of the game, but you will want to know what qualities they all have.
You get one M67 frag grenade at the onset. This is your stock generic grenade, so you know what to expect. It is worth remembering that this is the only grenade that can kill full health enemies. The 1st grenade you unlock, the V40 Mini, can be tossed at a much wider range, and you get three at once. Unlike the M67, it has a big blast radius, and can take as much as 80 % of the enemy’s health.
In general, the range and high damage of the V40 makes it a better option than the M67. However, because of the V40's range, you will have to learn an entirely different throw trajectory than normal. There are certain situations where it's easier to throw M67 immediately, so the choice comes down to preference and location.
RGO impact grenades have a smaller blast radius than V40, and you get two at once. Its larger damage falloff also leads to less damage in general. RGOs do detonate shortly after landing, but the tradeoff is just not worth it. Even worse, it also does not damage vehicles. In general, the need for precision detonations will be infrequent, so most of the time you don’t want to have this one.
M34 incendiary grenades, however, are even worse. You only get one at a time, and they cannot kill full health targets even at point blank range. They also have a short duration of explosion, leading to an weapon that’s just flat out bad.
M18 smoke grenades are what you expect from a standard smoke grenade, and for the most part, they do their job well. You get three grenades at once, and throwing one grenade generates a decently sized smokescreen, as you can see from the screenshot above. Throwing all three at once generates a sufficiently sized smokescreen to conceal movement. M18s also block spotting, so it provides an additional advantage.
The M84 flashbang only affects enemies centered at your crosshairs. Even enemies within your field of vision are not close enough. It does not daze, impair movement or block spotting. The flash it provides is brief and covers too small an area to be any good.
Finally, the handflare is luminous, but casts shadows when used to light dark areas. As a result, enemies are indistinguishable from surrounding objects. The handflare is no good for lighting up dark areas, and actually, the V40 is better at this job. However, the handflare is great at deployable concealment. It has a blinding effect, especially towards people looking straight on at it. You can use it to obscure enemy vision, while positioning yourself so you aren't affected. For example, you can be hiding under a couch and throwing grenades out towards enemies from the opposite end. You can also use it against enemies entering a hallway, like a smoke grenade. The flares also distract players in general, so you can conceivably enter a crowded room and use the effect from the flare to distract them in an instant and take them out. Some players will get used to it, so don’t rely on this last trick too much, but it’s a good one to have in your bag of tricks.