Welcome to the forum, Todd.
You will probably prefer a reader which does PDFs well, because many academic articles are stored in PDF format. However, philosophy articles usually have fewer graph or equations than physics and chemistry. So you might well manage with a 6" screen.
You should work out whether you merely wish to read articles and books, or whether you want to make annotations.
Do feel free to ask questions. Someone here is likely to know the answer. Also consult our wiki on the merits of different readers. There's a link to the wiki at the very top of this page.
And here's a direct link to the comparison matrix:
I also attempt to teach philosophy, when not campaigning against the imminent closure of my department.