For Surf City, you can take a bus on the main road just outside of the bus station in San Salvador. El Tunco is more touristic, if you prefer shops and all. Personally I prefer El Zonte. Fewer options...
"You'll find El Zonte to be very chill.El Tunco also has a relaxed vibe, but it gets much busier on the weekends. For shopping, El Tunco has a cool local store called Nekos Market and a dedicated smoke shop called Nomad."