Headcorn is good - its certainly got variety there:
Headcorn Aerodrome
Tiger Club (Based at Headcorn)
but for about the same walk from the station there is also The Pilot Centre at Denham (not to be confused with the others on the "South Side"):
The Pilot Centre (Denham)
I think you'll find Denham very slightly cheaper to hire from - but, of course, Headcorn is a much shorter trip to France.