depends aswell on where your to be going most nights?? if your wantin to go space(playa den bossa) or pacha,el divino (ibiza town) alot of the nights you are there, you would defo be better staying in playa den bossa,but if your going to be just going to bars or clubs such as eden/es pardis since its your first time on the island you prob be better staying in san an.Getting round the island from san an is easy also using the bus service/disco bus.
