Not to sound harsh, but how did you manage to get a job in ibiza for next year? (and doing what)
I don't understand how someone with so little knowledge (seemingly) of the island, locations, clubs+venues etc can work there?
By 'the other side' where do you mean? Playa den bossa, ibiza town..?
To answer your question, I'd suggest staying in San Antonio again, at least your familiar with it already (and if you don't already have a job lined up) I'd imagine it's a bit easier to find work there too. As for getting to the clubs etc I wouldn't really worry about choosing your location based on that, the island is so small, no clubs should be more than a 20minute bus journey, plus there's a couple of the big ones in San An.
For location think more about where your job is, you want to be as close as possible especially if you're going to be drinking while out there

you don't want big journeys to travel daily, especially at silly hours! Also, if your going working with friends, or already know some over there then it makes sense to stick nearby them.
Hope this helps and good luck8)
kenty