Assuming you are asking about fuel filters for automobiles, the answer is that it depends. A 10 micron filter will do a better job of filtering out larger particles from the fuel, but a 100 micron filter will do a better job of filtering out smaller particles. If your goal is to simply keep the fuel clean, then either type of filter will work. However, if you are trying to protect sensitive engine components from damage caused by small particulates in the fuel, then a 100 micron filter is probably your best bet.