PPE is offered at every college so there is loads of flexibility there in that you don't have to pick between 5 or 6 colleges, there's a really good chance you can go to one that suits you.
The "top division" is Balliol, St John's and Merton; which are very academic and are renowned for teaching PPE. Balliol's very academic but "cool" with it, known to be a bit left wing, only has college accommodation in the first and last year (a small amount for second years), but has loads of college housing elsewhere, very competitive for PPE - the most competitive by far. Merton has a very strong work ethic and they aren't really the most active in the university, quite rich; 3 years accommodation. St John's is exceptionally rich and has quite a high proportion of State schoolers.
Below that Magdalen is pretty good, probable has the best ground in Oxford, very pretty and they have deer; but are located next to the Cherwell - which mings; offers 3 year accommodation. Christ Church: old, prestigious, well known, rich, not as completive for PPE as most people think, 3 years accommodation. Worcester: has their own sport ground within the college which could be very handy; very nice college, quite apathetic, excellent food, only offers accommodation for 2 years. Wadham: massive, very liberal and active in the Union, only offer accommodation for 2 years (I think), state school. New College: musical, old, big, probable has the best gardens, accommodation for the entire course.
If you can try to get to Oxford and have a look around, those were the ones I considered when I applied.