It's not really as simple as what is the best, they all do slightly different things, but i think most will agree that F3 is the one most generally use.
And of course the light mapper crashed when you switch out of it to use the browser, it's an intense process that needs to be focused on the screen to render properly, it's highly recommended to let the light mapper do it's thing and not to switch windows and take the focus away, the same advice applies to most applications that are rendering too, Blender can do the same if it loses focus while rendering.
Primary Desktop:
i7 7700,k NV1070 8GB, 16GB 3200mhz memory, 1x 2TB Hybrid, Win10.
Secondary Desktop:
i5 4760k, NV960 2GB, 16GB 2333mhz memory, 1x 2TB Hybrid, Win10.
Laptop:
i3, Intel 4000 series graphics, 6GB memory, 1x 500gb HDD, Win8.1.
