Check out the Prices and Sharing section of
the guide, but these are also my thoughts:
39 week ensuites: probably for you not worth it, unless you want brand new stuff (Bluebell). Just forget about it. Will you use the extra 9 weeks? Probably not if you are in Brum. You are paying for 9 weeks - but at the ensuites you are paying £120-145/week for them (£1080-1305 'wasted') compared to the £774 'wasted' at Rootes/Westwood. If you get a 30 week let though, you have to move in/out over the holidays - what is the additional cost of that compared to having a room you can return to over the holidays and keep your stuff in?
Good locations for your degree (Biological Sciences): Bluebell, Rootes, Jack Martin, Cryfield, Benefactors, Tocil, Arthur Vick, Whitefields (anything south basically

).
Avoid: Westwood (big rooms though), it's on the other side of campus. And probably Lakeside as well.
So really, apply the location filter and 39 wk en suite filter and you get:
Cryfield, Whitefields, Benefactors, Rootes, Tocil, Jack Martin and Arthur Vick.
Cryfield is pretty much the best value for money. At £2280, no other halls comes near to beating it when it comes to annual price, although Whitefields is pretty good value for money as well, and you only have to move out for 2 weeks. Cryfield can be a bit claustrophobic at times - and the rooms are on the small side but you still get the basic stuff so it's fine if you just want that, pretty similar to Whitefields. There is the issue with the isolated Whitefields flats - it can make it difficult to find a new group of friends if you hate the people you live with as you will always have to leave your flat to meet others.
Benefactors sits as a strange hall - you will basically know all 70 people in the halls because there is one massive communal area, it's pretty cheap for an en suite as well (I'd say the shared room is well worth it if you don't mind sharing). Benefactors single: I'd be very tempted to pay a few hundred more for JM where you get a much better kitchen, but sadly forfeit the lounge. The Benefactors lounge was always a tip though whenever I visited it.
Rootes is pretty standard really - best atmosphere (in general) if you want to go out, facilities are better than Cryfield and Whitefields I'd say but still with the issue of high sharing ratios. Many people choose it because it is
the place to have parties, etc. But you get quiet and loud areas everywhere - it's just that there are more loud areas in Rootes.
Jack Martin over Arthur Vick, these two halls are useful for UK students who can move back over the holidays. They are essentially the same except that AV has wider corridors, larger rooms (probably by about 33%) and a lounge yet rubbish kitchens compared to JM. JM is considered by many, including myself, to be more lively though. Are they good value for money? You pay for the en suite, that's all I can say, it's only a few hundred more than Rootes/Westwood/Tocil across the year and perhaps the 9 weeks 'wasted' could be better spent on an en suite. JM you also pay for the great location.
Tocil you pay for the location (it's probably the best located halls of the lot) and the better sharing ratios compared to Rootes and Westwood. Beyond that I haven't seen anything special about it.
Apologies for the slow reply and possible gibberish. It has taken me a while to respond to this one.