If you want to park in Swindon or Cheltenham and get the bus in it's up to you - I've never done it but does seem convenient if it's anything like Farnborough. Parking is included with your ticket though so you can park on-site. Certain enclosures allow VIP parking closer to the grounds.
I always do the viewing village enclosure, as it has a separate area for photographers, separate food stalls and toilets. More importantly, you don't need to lug around seats with you on the trek to and from the car park making the day a lot easier. It all depends on how much you're willing to spend on the day really. Looking at the flightline, the enclosures take up the prime spots I think.
Last year's map is
here