LPB - a little distortion, but fairly clean
Rangemaster - more like a low-gain overdrive if you have hot pickups. Lots of Germanium mojo...
MOSFET - very transparent, too transparent sometimes.
All three boosters work well for pushing a tube amp into more distortion. For "solo" boost, the MOSFET boost is probably the best choice.
If you are using a solid state amp, the Rangemaster is completely useless.