I just wanted to say that, you shouldn't discount the smaller airfields that deal mainly in GA movements. Although at this time of year it is quieter due to the weather. They (we) can get extremely busy. We tend to have more runways available and encounter many interesting situations with novice (and more experienced pilots)
The College at Hurn, will teach you a complete mixture or traffic. But aircraft only ever join Downwind, overhead or occassionally straight in (VFR joiners). If an aircraft makes a mistake, the clocks are stopped and input told off. Pilots frequently make mistakes, whether it be lack of experience or unfamilarity of the airfield. (I know ATCO's make mistakes too).
Also you probably won't find lovely strip printers or ATSA's. So the workload is different from that of a larger airport.
If going for ATCO training, a broad mix of visits to different sized airfields will certainly be of benefit.
Good luck.