I'm think Clarence Dock is quite a distance from the University and so you might want to think carefully about that - you could be adding up to an hour or two commuting onto your day, and in winter when it will be cold and rainy A LOT. It'll also add to your travel expenses. On the plus side, it looks the most attractive setting.
I had planned to flat share with a friend that I met at college this year. Between us we could have rented a nice enough place in the centre for the same as halls. It was pretty unexpected for me when her application (radiography) wasn't successful. So my plans have been shaken up a bit late in the day.
R.e. Sentinel towers - I've heard the same thing: postgrads and int students. Possibly the best bet. I think all the rooms are en-suite, also.