My feeling is that
Full Sutton would be better. 15-20 mins away from York, by road, public transport to Full Sutton Prison
* - not sure if it stops nearer the airfield but as you are in York it won't be too difficult for you to find out. CFI is a member of the British Aerobatics Team and a very nice, helpful person and they have an aerobatic aircraft. Full Sutton also has the advantage of not being underneath controlled airspace but not so far away that you won't be able to get plenty of experience of it.
*As far as I can see the public transport has student rates but again that should not be beyond your capabilities to check.
Edited to add that it is also cheaper than Sherburn. Membership at Sherburn is £150/year, and at Full Sutton £90 - that's just for starters, hire rates are also cheaper.
Edited again to add that I forgot to give you the bus route number - it's 747 so shouldn't be too difficult to remember.
