I commute on 23's mostly because I also ride in triathlons. Otherwise, I'd probably ride on 25's or 28's.

However it's probably worth noting that if you're concerned about flats and ride quality, width is not the only thing that matters. Last year I picked up a set of Vredstein Fortezza's and the only problem I ever had was a slow leak. This year I've already got two flats (one my fault) on the stock Mondo Sports that came on my Specialized Allez. I knew the Mondo's were more flat prone, I just haven't gotten round to swapping them out yet.

So flat protection helps with flats. Threads Per Inch or "TPI" helps the ride quality. Of course the higher the TPI, the more expensive the tire. Dual or Tri-Compound tires can help with wear and grip.