It depends on whether or not you have a car, although some B&B's would probably give you a lift.
Horley B&B's (mainly on Masset Road area) are 5 mins away in the car. There is a cycle path that leads you straight from Horley into the CAA, it would take you 15 mins max. walking.
Crawley (town centre) is 5-10 mins in a car & the same cycle path will take you to the CAA, but 20-30 mins walk. If you stay in the IBIS, 10-15 min walk!
It all depends on your personal circumstances. If you have a car, have money, pretty confident of passing, I would stay in Crawley simply because there is more to do!
Horley has one main pub now, The Jack Fairmans. A Weatherspoons pub, cheap booze, cheap/good food & ok clientle! Other pubs in Horley, but pretty rotten!
If you need anymore info, let me know as I live local.
Maybe I should start up my own B&B for wannabe's doing the exams!!