Cambridge to me after several visits to both it and Oxford is just as exciting, lovely, etc as Oxford, though rather different. I could not chose one over the other really if I had to go to only one. Like Oxford some of the finest stuff is off the street and inside the college courtyards and museums and mess halls, etc.

Canterbury to me after multiple visits there on business is a boring city - oh a nice vibrant regional city with a thronged shopping street but besides the cathedral - reason enough for coming and its preceints - not much to make me linger at least. Perhaps twin a visit to Canterbury with nearby Chilham, a sweet village dominated by a lovely castle - rail service to both if going by train (I hope I have the village name Chilham correct!)

Manchester to me is a fascinating city - I went there primarily because of its Coronation Street associations but found yes a city with lots of great and eclectic museums - the industrial museum is topnotch - it also has one of the world's oldest train stations that is now part of a municipal museum where you learn about, of all things, the city's sewage and drainage system in subterranean areas - check out the Salfaord Docks area too for contemporary modern buildings in a wide port area.

Newcastle I have walked around a few times and never was struck with any need to linger though perhaps like Manchester you have to take a closer look and not just see a rather blah city overall IMO - though in a smashing great setting of rivers with cliffs bisecting it.