El Salvador lacks luxury resorts along the line of Mexico, Costa Rica or Caribbean locations.
Tesoro Beach gets mixed reviews. The facilities are a little outdated but the location is great and the food is not bad.
Royal Decameron is an all inclusive also with mixed reviews. Some people complain about low quality of food or facilities.
I would consider an Airbnb in the Costa del Sol. Be careful because there are lots of older properties and I would read the reviews very carefully. I would pick something newer; there are several nice new apartment buildings or townhouses on the beach - some with ocean views.