Modern bicycle theory says you don't (get power on the upstroke) That is basically an urban myth.

http://www.bikejames.com/strength/wh...-stroke-power/
https://roadcyclinguk.com/riding/bik...wXxkk8i7LSI.97

As for pedals in traffic, I would suggest you go with whatever you feel more comfortable with. I use a modern shimano clipless MB system that allows me to unclip and clip in very easily so I don't feel trapped as some riders do. But I don't ride in heavy traffic either.