I believe that the 50 grenades 10 RPG the best tactic in GTA online, Because it is the easiest, and most effective way to get kills, with the least resistance. The 50 grenades 10 RPG is universally known as the best GTA online tactic by gamers. None of the others come close in terms of effectiveness.
I am not a GTA online player, but I have years of experience with online gaming. A player should just use grenades and rocket launchers (RPGS) to get all of the "kills". While they are not technically cheating, it is quite unfair as an instant hit with the explosive is a guaranteed kill, as opposed to a competitive shootout.