A few years ago the NFL players survey rated FieldTurf just behind natural grass in preference, though at that time I believe there were still some of the old style Astroturf carpets around that were the most despised. Taking a look at the 2010 survey, which was basically between grass and FieldTurf/infill, grass was the winner.
But there are a couple of other angles: 1) recruiting, where I wonder if there's a perception that FieldTurf is new and cool (and grass is old fashioned); and 2) durability, where some grass fields haven't held up well (Iowa and OSU for two, though a big chunk of Iowa's problems were caused by trucks when the new south end zone was built).