Stratford on Avon is a nice location, the hotel is central if you do not have a car, easy walking distance into town, and there is a river boat trip that leaves near the HI car park. Stratford on Avon is also one fo the few HI's that seems to be good at Plat upgrades.

If you have access to a car then the CP at Heythrope Park (North of Oxford) is nice, fairly new and really nice rooms also near Blenhiem Palace, but not one to do without a car.