A 24 inch wheel will give you a slightly higher amount of torque and slightly lower top speed, a 26 inch wheel will give you slightly more speed and slightly less torque. The bigger the diameter of the wheel, the more speed and the less torque. If you live in an area where there arent many hills, then torque is not as important. According to my research (which could very easily be wrong, but its all I have to go on at the moment), wheel size affects speed at a rate of about 1mph per inch of wheel diameter. Therefore, a 24" wheel will go roughly 2mph slower than a 26" wheel, but will have a slight torque advantage over the larger wheel. I run a 26" wheel myself.
