I very nearly ended up at Warwick for Postgrad so I have a reasonably good idea of the department. A relatively small department, which doesn't have much neurosciency/scanner/animal stuff at all, but is very strong in the stuff it does do. Of the four, York certainly has the best reputation, but they're all good so go and see which you like for yourself.
As for the PS, look on the site's wiki and there's quite a few example statements on there. Then of course, when you've got a draft down put it in PS help and we can give you feedback and advice.