I lived in Ranmoor during my Master's programme, but I did spend some time in Endcliffe as it's literally down the hill from Ranmoor. What exactly are you looking for? As a postgraduate, you have access only to some buildings allocated for postgrads (51 weeks) in Endcliffe and Ranmoor. If you're looking for more entertainment, then I would say go for Endcliffe. You would be surrounded by a lot more undergraduates and the Edge. Ranmoor is a lot quieter of the two. However, both are very close to one another.