I've ridden from 700x23 to mountain bike tires and everything in between for commuting. Of course, it's hard to remove the variables of the wheelset weight and bike weight. But I found 700x28 to be ideal for me for fast commuting. A little lower PSI adds more comfort without much hit on rolling resistance or weight. But it adds a level of security for me too, not sure why but seem to flat less with wider tires. I loved my 700x28 Gatorskins.

Conversely I'm running 700x32 Marathon's right now. They feel much slower. Heavier, harder to accelerate, sluggish. But, like I said, it could be other factors. I can't wait for them to wear out so I can go back to 28's.