What do you want out of your time in Ibiza?
Santa Eulalia would offer you a very relaxed time, with lots of nice shops and resturants to choose from serving a high standard of international food. It's a mature atmosphere, although we are in our 20's as well and always choose Santa Eu. The beach is probably the best resort beach on the island. There is some live entertainment in Santa Eu but no were near as much as other resort towns, people really do go there to kick back and enjoy a drink and a meal and soak up the Catalan culture. If you plan to go self catering than the town is a good choice as its as much a residential area as a resort town, meaning the shop are good value and there is a supermarket, which is obviously a good place to get beer and wine. The town also offers excellent (in the summer 24 hours a day) bus routes (
INVALID URL to Ibiza Town and Es Cana, if you did fancy a more active evening one night.
Ibiza town is a livily place, full of really nice bars playing up to date dance music, as well as the old town with it's late night markets and boheimium feel. It also boosts a nice marina area. There are a couple of the clubs here, Pacha and El Divino - also Priviledge and Amensia nightclubs are a short bus / taxi ride away.
Es Cana is a very British family restort, which does what it says on the label. Don't expect much in the way of Catalan infulenced culture here, but you will find a very popular beach with watersports, as well as many British bars and cafes serving up full english and chicken and chips.
San An offers you Eden and Es Paradis nightclubs as well as sun set strip which is home to Cafe Del Mar and Coastline Cafe, which is a nice place to hang out and watch the sunset. Unless you like watching 16 years vomit in their shoes at all times of the day, avoid the West End, its the part of Ibiza you see on programs such as Ibiza Uncovered and is appalling - time it was closed down IMO.
Playa Den Bossa, is also a family area outside of Ibiza Town and is home to the big waterpark and Space nightclub.