If all other variables are equalized, a larger wheel makes fewer revolutions for any given distance; therefore the friction in the bearings is reduced accordingly. So yes, 700c rolls a little faster. But while rim size is one isolated variable, your rolling speed will be determined by many-- tires, bearings, aerodynamics, road surface, etc. Beyond considerations of tire availability, I would not consider wheel size a major factor in a decision about buying a bike unless I was looking for something very specific, such as the smallest possible folding bike (in which case I'd recommend 16", but that's for another forum).