Oxford, England

Oxford's City Centre has sightseeing (particularly if you're an art, history, literature or architecture buff), shopping, restaurants, pubs and more.  You can easily spend 2-3 days at Oxford and have a wonderful time.  We chose to stay in Oxford during this trip because our daughter was studying at Oxford University.  The one drawback is that few sightseeing tours originate in Oxford - although the tour we took to Salisbury, Old Sarum, Stonehenge and Avebury was very good.  For visiting Oxford and other places in Southern England, the better place to stay is London, as there are a great many tours that originate there.  Plus, while we saw a lot in a day, London is clearly a 3-7 day stop, depending upon how much you want to see.

When we come back to visit Southern England, we plan to visit Oxford again, spend a few more days in London, and also take day trips to Bath, Stratford-upon-Avon, Isle of Wight, Warwick Castle, Windsor Castle, Blenheim Palace, and York.

Here are some helpful websites:
Visit Britain 
Oxford University Colleges and Halls 
Map of Oxford's Colleges and Halls
Streetmap 
London Underground (The Tube)