I've been commuting 22 miles per day this summer using platform pedals and tennis shoes. I've finally got comfortable enough with my route to switch to back to clipless.

I do prefer the clipless. Speedplay Zero's on my road bike and SPD 2 bolt mtb on my recumbent. Of the two, for commuting, I would recommend the SPD and some good rubber soled mtb shoes with good gripping soles. I wear SPD sandals. Road shoes tend to be a little slippery if you put your foot down in hurry.