Pros and cons as I see them;
Magnetospeed - great for crowded ranges, easy to setup behind firing line. Not so great when chrono-ing(?) multiple rifles compared to other units which are setup independent of the rifle.
Lab radar - Cadillac. Sits at the shooting position, so setup is trivial. Can be confusing with many people on the firing line, as radar picks up other near you and returns results. Has trouble reading fast stuff >3900fps
Two-Box - requires down range setup. Provides very accurate readings in a 6'x6' 'window' allowing one to shoot different targets without fear of misalignment. Good compromise between optical and radar. Has trouble reading slow stuff <1200fps
Optical - needs to be setup down range, needs precise alignment. Danger of shooting sensors or brain. Concerns with direct lighting/sunshades. Some units of lesser quality do not provide precise results.
*edited lab radar speed limit to 3900fps as per mfg, got my numbers mixed up off the cuff