Hey, I'm living in one of the halls now, so hopefully I can offer some insight!
It really depends on what sort of atmosphere you're after. And remember, that while I can tell you what the halls are like this year, and they do stay relatively the same, the atmosphere really does depend on the people who attend, so it can change. But still, I'll give you a bit of an overview.
Halls with good balance of good social life/hall functions/still some quite residents so that it's not too unusual if you want to spend more time studying: Richardson, Roberts, Howitt and (maybe) Farrer. In my opinion, if you end up in any one of these halls you'll be ok.
Richardson and Roberts halls are interconnected and used to be the same hall. They are both around 5 stories high and grouped into stairways where there are about 4 or so rooms on every level and maybe 7-9 stairways in the hall (depending on which hall, Richardson is slightly bigger). Both of these stairways have kitchenettes and a bathroom on every floor level and a separate communal kitchen and common room which are used by every stairway. This is the best set up, in my opinion, as it allows for more socialisation with the entire hall and not just those who end up in your stairway/level.
Howitt is the tallest hall with around 11 stories. It actually has an elevator (which has a bit of a reputation for breaking down). In Howitt, you are grouped into floor levels and each level has its own fully equipped kitchen/bathrooms/common rooms. Residents from Howitt have a pretty good social life so again, it's one of the better halls.
Farrer used to be known as the party hall, but seems to have quietened down over the last few years. I don't know too much about the set up there unfortunately, so I can't offer too much more information.
The halls which are known for being quite/study centred are Deakin/South East Flats/Jackamos/Briggs. The last two are self contained units and do cost a bit more. As they were only built last year, they have not yet really developed any traditions and don't have a hall society to organise any functions. Deakin apparently has slightly larger rooms than the other halls (other halls over pretty decently sized rooms - you'd easily be able to fit a bar fridge, it comes with a bed/desk/chair/various other things, so you will have plenty of room regardless), but is known for being very, very quite.
Choose wisely.