From personal experience, I can say that if you don't want to use Vsync, then you should use high or benchmark. Benchmark will simply unlock the framerate cap and high will impose some kind of a framerate cap but it will keep it lower.
Honestly, LoL' framerate cap is the worst I have ever seen in a game. There's something wrong with the game engine and how it deals with the framerate. The framerate locks 30FPS, 60 FPS and 80 FPS don't work as they are supposed to. For some reason, if I choose 60 FPS lock, then the framerate just jumps around 45-60 FPS, even though I can achieve 180 FPS on benchmark.
So my suggestion is to disregard 30, 60 and 80 FPS locks and just try high or benchmark. But if you use Vsync then the fps locks don't mean much since Vsync will lock your framerate to your monitor's refresh rate, either 60 or 120.