for what it's worth san antonio is my favourite night out destination on the island. its bars have a diversity and provide good entertainment at reasonable prices which just can't be found anywhere else in ibiza.
we head for the area round the church where we can eat and drink and listen to really good live music for free and with completely normal bar prices. i like es verro, don quijote and cafe babel in particular, and usually villa mercedes and the island cafe are on my itinerary at some part of the evening too.