Hiya I'm a current student at Surrey and I lived in Stag Hill during term and then moved into Cathedral court over the summer (I have a teaching job in g.ford).
Cathedral court is in my opinion the worst band C accomodation of the lot. The kitchens are tiny, in most if not all other halls you get one large and one small cupboard for food/crockery storage in the kitchen plus a shelf space in the fridge and in most halls a shelf space in the freezer. In Cath court there is only 5-6 shelves in the fridge/freezer and you get 2 small cupboards, if you're lucky one big, one small. The kitchens are definitely 'cosy'!!!
Cath court halls are also one of the last to be updated, they're due to be renovated next year and as a result some houses are in need of a bit of a repair. My room this summer had a large recurring black mouldy patch on the ceiling above my bed due to the flat roof leaking...niiiiice.
Stag Hill is often overlooked as it is so close to the union, I lived in the second row of houses and wasn't disturbed by the noise, yes you can hear the union, (particularly on 'bling' RnB night!) but its not a loud enough level to keep you awake. Stag hill is popular because the rooms are divided into pairs and each pair (of the same sex) shares a bathroom. The bathrooms are literally outside your bedroom door so it makes it practically ensuite, much better than sharing 4 toilets/showers between 14 as in Battersea/Surrey court.
There are some Band C rooms (non-ensuite) in University court but there aren't that many so tend to get snapped up quickly. I think you share two bathrooms and a nice newish large kitchen between 5 or 6 people.
Whether you take an ensuite room or not is entirely up to how you feel about sharing showers/loos with a large number of other people.
The liveliest halls of residence are probably Battersea/Surrey court.
With reference to being close to the central hub, Cath court isn't really the most central - Battersea is probably the closest to the centre of campus. Cath court is really convenient if you're a PATS student (Music/Dance/Sound Recording etc) and is the closest to the library and the laundrette.
Twyford, International House, Millenium House and University court are the newest halls of res (on campus) so are generally the nicer looking, better condition halls.
Stag hill and Surrey court were being renovated over the summer so should be in good condition (i.e no mould, new fittings etc) for 08 freshers.
Hope this helps!