Another vote for Speedplays.

Double sided entry makes is much easier to engage.

You can unclip but keep your foot on the pedal, ready to stop, when you are going slow, in traffic, or even pedalling uphill. I use this a lot - unclipped, but still able to pedal is a big plus.

My knees have never been happier!

(I use the Zeros with adjustable float - but more important - adjustable release angle. I have it set so that I can release very quickly)