I think either a Kindle or a Kobo is a good choice if you want to read classics. Either store will give you all the free classic books you're likely to want in the correct format. You can also get them from Project Gutenberg in either format, also free, and from a number of other sources.
Personally I prefer Kindles but Kindles and Kobos are both excellent. I have both and I use both.
If your need for PDF is also because of your classic reading you can probably forget PDF. Everything in classic books is available in mobi and epub.
If your need for PDF is for some other reason I'd consider getting a 9.7" or 10" tablet of some sort. Kindles and Kobos will read PDF but you need a larger screen because in most PDF's the text doesn't flow. Reading most PDFs on a 6" screen is pretty difficult.
There are also larger e-ink readers but they're expensive and I don't know much about them. They might be worth looking into if you don't have budget limitations.
Barry
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