In making a decision between steam-driven and pump-driven units the pros and cons of each must be considered. A steam-driven unit costs less than a pump-driven, but because steam units cannot produce the high pressures you need for proper extraction, they often only produce a very strong coffee. The boiling process also tends to scald or burn the coffee grounds. With this type of unit you do not have the frothing capabilities that you have with the pump-driven units.
While pump-driven units costs considerably more, most pump-driven units provide the needed temperature control and pressure for extraction of the cappuccino.