I have just recently done a lot of research into this subject for the same reasons and offer the following:
West Byfleet - definately the best patch for London for all the reasons articultaed. However, highly sought after, long waiting list and difficult to see how you ever rise to the top of it within the 4 months they allow you to be on the system for before your posting start date.
Biggin Hill - plenty of availability but very remote and rural
Kingston - 70s town houses that Mrs AW and I didn't take to. Due to NATO population, turnover a bit sparodic
Uxbridge - modern houses but behind the wire of a base literally falling down. Plenty seemed empty but the development of the old base starts this year, so probably not the most pleasant place to live in the short term
Bushey Heath - Bushey = dump, but the SFA have been sold off there. Bushey Heath seems very nice, although there is evidence of under investment in some properties. Nice quiet patch set in an expensive looking area and Stanmore tube only 4 miles away(just over 30mins to Westminster). Reasonable turnover here - we have been allocated a house for the summer that will be vacated in a few weeks.
Hope this helps.