Master Keyer: good catch all, and my general starting place--tends to be the best/easiest for actual green/blue screens. Does a solid job with soft detail. Not very helpful with desaturated colors though.
3D Keyer: Better for desaturated stuff because it takes the luma value into account. Often gives a very noisy and more unpredictable result than others.
YUV Keyer: Good with bright stuff like the 3d keyer, gives nice softness generally.