Not that many people really tend to stay in Ibiza Town. If you're looking at being nearby, I'd look at Talamanca or Figueretas/Playa D'en Bossa. All three are within a half hour walking distance or you can get a bus or a boat for not very much.
It really depends where you're planning on spending most of your time. I've never stayed in San Antonio but it's the cheapest resort and you've got the Sunset bars and some decent restaurants (Curry Club, Villa Mercedes). If you're going to any of the nights at Eden or Es Paradis then you'll be well located.
Personally, I prefer the other side, near Ibiza Town as that's where I spend most of my time, be it for the bars, restaurants, beaches and clubs. But if you're going to hire a car, it doesn't matter so much where you're based.
