I ride both 700c and 26" while commuting (different bikes!) and feel that either are just about as fast, maybe 10 percent faster on the 700c wheels. HOWEVER, for cushion, bombing around city debris crap on the roadway, and tire stick, fat (2.1+) semislick 26" tires (slimed and mr tuffied) is the best way to go. A long commute on smooth roads in the country or rural areas, probably 700c is a good choice, or distances over 10-15 mi each way.