Visually I rate Oxley the best of the halls, its in lovely grounds and it does have one plus over all the others in having its own gym. In terms of the social side of the hall itself, Oxley has its own bar where Lupton doesn't. However, Lupton is in prime location not only for shops but socially as well it is in the middle of Headingley so there are a lot of good bars, pubs and cafes within a 5 min walk from Lupton. Because of this I would say socially Oxley people know more people within their own hall than Lupton do, but Luptoners will get to meet a wider spread of people from other halls and 2nd/3rd years living out in the nearby area.
Location is the main downer to Oxley, because you have to do your shopping in the same place as the Luptoners (Headingley Arndale Centre) but its a 20 minute walk down, although you can get on a bus and they are quite regular. Given that you will be wanting to go to uni and town on the bus though, you will need to get teh more expensive bus pass if you live in Oxley or Bodington because it is outside "Green Zone"....if you live in Lupton you can just get the "Green Zone" pass. The difference in price is about £20 on a termly pass I think. However overall the bus pass is still well worth getting and becomes excellent value for money when you use it to travel down to and back from nights out in the city (they run till 3.15am), think of what you will save on taxis with that. If you live in Oxley though you do need to make sure you get the last bus back, if that means you're in a club open till 3am then I would say try and leave at 2.50 because there's a risk that if you're waiting to get your coat back from the cloakroom, waiting for a drunk mate in the toilets etc you could end up being delayed and where Luptoners will just have a sober-up walk home (25 min from Lupton to uni, so about 35-45 min from town depending on where you are), you would have to add another 20 min onto that for Oxley which can make it quite daunting, and if you miss the bus then you are going to be on a taxi.
Security wise they are both OK but I would say Lupton is safer as the bus will drop you at the Arndale centre which is literally round the corner from your residence. In Oxley you have to walk a few minutes down a path which is a little secluded, its a nice area in the day but it is not very well lit at night and can feel a bit eerie.