In my opinion, the Hilton Hotel brekafast is the best in Santo Domingo. This is a buffet style breakfast with serve to order egg's in any form you wish with all the freshest fruits and freshly squeezed jucies in town.
I've been to Marocha, Melia, etc .. but the Hilton beats them all for the "Complete Service". If I remember correctly, its $500 pesos for the breakfast buffet that is served everyday of the week with excellent service and a beautiful view of the ocean.
You won't be disppointed and you'll probably be a repeat customer.