I know you will receive excellent advice from the TE pros, but I'll chime in with my 2 cents. I have a bad knee and I use Speedplay Frogs on my road bike and mtb. The Frogs (and other Speedplay pedals) will allow a greater degree of float than many other types of SPD's and I can easily unclip with them. I also use Wellgo platform pedals with pins on my mtb and it allows me to change my foot position easily. I use the platform pedals when I exercise the dogs on my mtb.