I am in Santorini now with my husband and we are staying at Ikies House in Oia. We have been here three nights and absolutely love it. The view is amazing, we are centrally located to restaurants and shopping, and the staff has been very accommodating and helpful. I will post a full trip report when we return to the states, but I highly recommend Oia as your destination. Fira wasn't as pretty, although all of Santorini is amazing. I am convinced we are in one of the best located hotels here...it is breathtaking.

Last June we stayed at Sunny Villas in Imerovigli. The view from our terrace was impossibly beautiful. I'm sure that can be said for much of Oia as well. I enjoyed spending an afternoon in Oia but it was nice to get back to a more quiet setting. Imerovigli is more laid back than both Oia and Fira. If you are looking to walk out your door and find endless choices for drinking and dining Imerovigli is not the place. Having said that, I would go back there without hesitation. There are a few restaurants and it is and easy walk to Fira, 20-30 minutes.
Enjoy. It will be hard to go wrong.