The SJT (Shanghai Jiao-Tong) listing appears to be the most reliable, although it is weighted towards those universities with outstanding research in the sciences.
As for Oxford, I was only there for a term, but I think it's one of those places you either love or hate, but I would presume that the differences and peculiarities of Oxford vs other unis is far less pronounced for postgrads than it is for undergrads. If there's a project you like, and the reputation for research in that area is good, then go for it!