I used Shimano SPD, SPD-SL, and Speedplay Frogs. I love the Frogs the most when riding in urban settings. There is no metal spring in either the pedal nor the cleat. It used a elastomer on the cleat to engage the pedal. Instead of stepping on the pedal to engage a la SPD, you slide your feet onto the pedal. Frogs provide a lot of float (~20 degree) and because of that, you will need to twist your heels out more to disengage. Since there is no spring, there is no resistance when you clip out. It helps if you have some sort of knee problem.