The economics department at warwick is amazing, arguably better than the one at Oxford. Yorks economics department is great, but not up there with the top 5 (Cambridge, LSE, Oxford, UCL and Warwick [in no particular order]).
It isn't a matter of are they as good overall, it is a matter of what you prefer.
If you prefer economics major then Warwick is quite possibly the best out of all three. Its economics department is either on par with Oxfords, slightly better or slightly worse. Also the mathematics with the Warwick course is far more flexible: at some Oxford colleges (at least when I considered applying) if you do not have A level maths you cannot keep economics in the second year - this may have changed now although it was certainly the case a few years ago.
However at Warwick the maths is taught as such that you can come in with only an A at GCSE maths and still end up doing econometrics and majoring in economics (although it is rare and a lot of work it certainly isn't impossible).
If you prefer politics and/or philosophy then Oxford is by far the best and York might outrank warwick, especially in philosophy.
Also one thing brilliant about the Warwick course is that it is very easy to switch to pure economics, pure politics, pure philosophy in your second year should you wish and many people do it. This is not the case with Oxford and York so the Warwick course offers the most flexibility.
Having said that Oxford's is by far the most prestigious and you should go for that above all. However if you are especially interested in economics then Warwick PPE is quite possibly superior to any other university's PPE course in the country.
I researched this very throughly when I was thinking about applying to university and whether to go for PPE/ economics/ SPS/ philosophy/ philosophy and economics/ politics and economics.
From what I have heard: Warwick's course is thought of in industry as more prestigious than all but Oxford's with the economics major pathway because it is an exceptional university for economics. However in academia Oxford's is thought of the best and general opinions may differ, but Warwick economists are in very high demand and PPE with an economics major pathway at Warwick doesn't seem to be seen as being that different from people doing a full economics degree by those in industry.