a friend of mine just returned from a weekend break in Manchester shopping in the Trafford Centre. Her and hubbie stayed in hotel right beside it and were able to pop back with the bags every so often. She said the shopping centre was fantastic and they'd a great time as in the evenings there was plenty of restaurants at it to choose from. So if shopping is your thing then that comes recommended! Personally I'd prefer London as it's more varied, has great markets (Shoreditch, Spitalfields etc) and some museums to vary the day's activity.