The skinnier the tire, the more flats. I get about two a year on my road bike and none on my mountain bike. If a flat would totally screw up your day, get a fatter but slower tire. If a flat is something you can easily repair on the road or you don't mind locking the bike anywhere and hopping on a bus or in a cab to complete your commute, then get the skinnier and faster tire. And keep it pumped up to avoid pinched flats.