If you are a paying family of 4 the shuttle price, round trip, would run you $64.00. The $16.00 round trip is a per person rate. The taxis stationed on the site would be able to pick you up whatever time you desired, take you directly to Universal and than bring you back to the resort at whatever time you desired. The taxis vans hold up to 7 passengers at a price of about $35.00 each way.
Taxiing is much easier and directly back and forth to Universal, no extra drop-off or pick-ups while you are riding. You would still have to pay the approximately $35.00 with one, two or three passengers. The time to Universal would be 25 minutes in a taxi compared to a possible 35 to 60 minutes in a shuttle, depending on where they have to pick-up or drop-off other passengers.
You don't have to call ahead and reserve either way, just walk out and pick up the taxi.