Keevil is great but a little restricting, old airfield coned into a circuit. Any form of racing or dodgy over taking will get you black flagged as me and captain will tell you.
On the other hand it is cheaper and very safe and still really good fun for testing your car, you can google some vids which will give you some indication what the circuit is like.
Castle Combe, only been a passenger there, the run off sections scare me, but I really do like the track, much more of a drivers circuit and more exciting to drive imo.
Hope to be there where ever you choose.