andy,
for general great times out and about and nearness to the sunset cafes, san antonio is your best bet. try the Sol Bahía for apartments or the Gransol if you prefer a hotel
if you wish to be near space and bora bora, then you want playa den bossa. look no further than the jet apartments, which is very popular with groups of clubbers
if you fancy living in cosmopolitan surroundings, then go to ibiza town. it will probably be a bit more expensive, but you are right next to the port area which is the most exciting bit of the island at nights. for real class, try anything in the marina - el corso, argos, or a bit cheaper are the el puerto apartments in town
if money really is no object then go rural with one of the luxury country hotels. can pere and can lluc are both 10 minutes drive from ibiza town and offer the absolute height of luxury.
if you wish to sleep with vips and celebs, try pikes ;-)
all of the above can be found in the
hotel guide on this site. click on link at top of this page.
most of the hotels also have reviews, which gives you a good chance to read about other holidaymakers' experiences.
good luck