I agree with Ex-pat....
Definitely Papi's (La Casita) for either shrimp or lobster. Papi's are famous for their shrimp skillets absolutely loaded with large shrimp in their garlic and tarragon cream sauce. Certainly the best value on the beach considering the quality and the amount. The lobster is also available in the same sauce but I tend to stick with the shrimp.
Los Locos del Frente is the best place in town for steak. Very reasonably priced, but there is only one type of steak. Always tender and char grilled. They also have the best pork chops in town, big thick juicy chops, there is nowhere else in the area where you can get pork chops like theirs. The only thing is you usually need to get there relatively early as the place is small and fills fast. They also run out of various things early....just about everytime I have gone after 8.00pm they have ran out of something, usually the pork chops....also, the service can be terrible at times, definitely a place for the food, not the service, but it also depends on the night. Just don't let the crazy chef serve you!! Haha. It is actually one of my favourite restaurants off the beach.