Hi AliH
I'm a bit of a health farm junkie and have been to quite a few of the biggies for the day courtesy of my lovely DH and his very generous crimbo/birthday gifts!
I have only ever been an at Hoar Cross and Inglewood and loved both of them.
They are very different though IMHO, Inglewood is very relaxed, homely, unpretentious, friendly, lovely therapists many of which have been there for years which is a very good sign. Two excellent male masseus (sp?) there who are a laugh and say all the old deeries end up chasing them! Best thing about it is that you can go out on an Inglewood bycicle for a tour of the village and accidently visit the pub and the great bakers in the village!
HCH is totally different, but not necessarily better, it is very swish and much more , it definately has better food, its a much more stunning building it has some good therapists but quite a high turnover of staff when I was there last
RobinW, Inglewood is one of the cheapest and Champneys is one of the most expensive, your are looking at minimum £100 for a top-to-toe day. They all do really good offers and the best thing is to phone them all, get on their mailing list and you'll hear about their cheapies.
I second what Ems says about go close to home or get someone else to drive you there. My favourite top-to-toe day was at The Sanctuary - absolute bliss and worth every penny, my second the spa at the Runnymede hotel and the worst was Sopwell House but they were in the middle of a massive refurb so it may be better now.
If you're close to town robinW the elemis spa is meant to be excellent but I've not had the pleasure of sampling that one yet!