Sorrento, without a doubt ! But make sure you are in the resort, rather than in some hotel outside it, as you will be spending time in minibus coming and going to the centre every day.
I have stayed in this place 3 times over the last few years ::
http://www.villaggioverde.com/
You will love Pompeii ! Take the train from the station in Sorrento. You will be travelling with lots of locals....kids on their way to school, Mums doing their shopping, etc. The train stops just outside the entrance to Pompeii. If its a hot day, take sunhats and sensible shoes !
take no notice of people that tell you not to go to Pompeii....its an experience of a lifetime !
Make sure you go on the hydrofoil to Capri....probably one of the most beautiful places in the Med. Again, like Pompeii, ignore all the excursions sold by the tour operators....just go down to the Harbour and get on the Hydrofoil.
The journey across the Bay of Naples is wonderful.