I can't make specific recommendations (because I am an iPad user
), but I would just say that I'd strongly recommend that you look for at
least a 9.7" screen to be able to comfortably read PDFs without endless zooming and scrolling. I read an awful lot of PDFs, and find the 10.5" screen of my iPad to be an ideal compromise between size and portability.
I don't think that high resolution is particularly important, but storage space is, because PDF files can be really,
really big. If you get a device which has only 8GB or 16GB internal storage, I'd make sure it also has an external memory card slot to allow you to carry around a respectable number of PDFs with you.