I'm no expert on Salvadoran food but Estrellita's pupusas are what I dream pupusas should be. I've eaten twice at her booth at the Sunday Alemeny Flea Market. She pats the masa and fillings into a thick pancake and grills them while you wait. You get them light and slightly crispy with the cheese melted and hot, topped with curtido and 1 of 2 salsas.
So far, I've had the mushroom, which is intensely earthy in the same way as Gioia's mushroom slices. The cheese is chewy with sort of a Parmesan tang to it.
I like the mild salsa with jalapeno slices. I didn't think the hot was that hot or flavorful. Yesterday I asked for a Loroco, but either its flavor is extremely subtle, it's an ingredient of all varieties or I just got a cheese pupusa. Nonetheless it was very satisfying but cheesier and milder than the mushroom
Estrellita sets up shop every Sunday at Alemeny. She will be at the SF Street Food Festival this weekend.
Also at Alemeny is Huarache Loco (From DF to SF). They have a full battery of taco fillings including Alambre, which is basically everything but the kitchen sink. It was good but not in the same league as E's pupusas. There is also a "roach" coach which has a few Filipino specialties.