You should not choose... Your plumber should do a code "Fixture Demand Load" study prior to pulling a permit to install the water supply line and the code will define the required diameter of your supply line. The meter should then be sized equal to the supply line. The exception is 3/4" is the minimum size permitted for a supply line, but in instances where the fixture load demand is minimal, they may opt to install a 5/8 meter on a 3/4" line.