Look Keo are pretty popular but don't have as large a contact area as Shimano though they are lighter than Shimano pedals, however the Keo line now has the Keo Max 2 which has a wider contact area. Speedplay is a good choice if you want a good variety of float to choose from, if I'm not mistaken you can adjust it up to 15 degrees; this is especially helpful for people with knee issues. Keep in mind that with Speedplay the mechanism is in the cleat itself rather than the pedal.