I fly both types on a fairly even basis. I'm convinced from the actual reaction of friends, family and prospective passengers that the biggest single factor in PA-28 sales has been the appearance. "Oohh, it's just like a real plane" I can hear them say.
The 172, on the other hand, is sometimes greeted with incredulity. "You fly in that?" is an authentic quote.
So which do I prefer? In America, I love the 172 for its sightseeing properties and camera friendly opening windows. In UK, I love the PA-28 for it's huge luggage bay, able to take the largest computer system, and the confidence it apparently instills in relatives.
In almost every other respect I find them indistinguishable!