There's no such thing as "good" and "bad" halls - it all depends on what you're looking for and on the people you live wth, but if you don't like it, you can always ask to be moved. Also, it's not necessary if one hall is social this year to be the same next year as well... Childs, Stenton and Mackinder are basically the same for the inside, and are so close to each other that it does not really matter where exactly you live in regarding the vicinity to the buildings. I have no idea which hall is bigger and which is smaller, but the premium en-suites are usually different blocks 3-5 floors, with 2 or 3 flats on each floor, the flats have 8 or 10 rooms, depends. If it's important to you, just check the accommodation website, I think that it was written over there how many rooms has each hall.
I am self-catered and I know some people that are catered... well, it depends really on what you want. I can't cook very well, but I preferred it because it's cheaper for me to buy groceries from Asda or Tesco or whatever for 2 weeks for less than the money that the catered students have on their card for a week... if you're not catered, you can always buy things from the eating places if you want to. The problem with the catered as far as I know is that they have only microwave in their kitchens, so it's not very convenient if you want to make something sometimes, but again, there's no right answer, everyone looks for different things, but personally, I think that it's cheaper for the self-catered, at least it is cheaper for me that way - but it depends on your lifestyle and eating habits as well.
If you want to ask anything in particular about the halls, feel free to write me, good luck!