Python, I've had only used spd pedals for years, but decided to change since my last set of cheapo spd have been hard to clip in and out, plus my knee has been hurting. My new speedplay frogs are so easy to get in and out , I've only rode with them 70 miles, but definitely feel like they will be a winner in my book.
Some people with knee issues find the float easier on their knees. The mountain bike pedal allows you to use a cleat and shoe that is walkable. I was worried about the change since I am such a klutz, but felt like I could handle it after the bike shop set my bike on a trainer, so I could practice clipping in and out. Sometimes just placing my foot on the pedal was all it took to clip in. A miracle after my experiences with the spd's. There is many pedal options, but hope you can find the right one for you.