Personally, I find that it depends on the subject.
For example for Maths, Psychology and languages past papers are very useful but for English, history and subjects like that notes are really good.
I think that possibly the 1 subject in which both is probably very useful is science (especially Biology and maybe Chemistry) although physics is mainly graphs so past papers are good for that.
Basically, I do past papers when I'm running out of time and don't have the patience either to make notes.