For reading books, etc I like and use a Samsung Galaxy tab 7.0 plus. Samsung doesn't update system software often if that is important, maybe twice in three years. For games, data entry and video watching I I like and use an ASUS 10.1 MEMO. I haven't barely tried 8" tablets, if they fit your hand that might do for reading, but 7" size may fit in your pockets slightly better or however you plan to carry it.
I would recommend a resolution above 1024 x 640 for 7" size and 1280 x 800 or above for 10" size. Your taste and eyes may vary. If all your doing is reading documents and reading e-mail, and lite web surfing a dual core cpu is fine.
If you are into gaming, encrypting your data or other things that makes the processor a quad core cpu would probably be better. If you can borrow several of different sizes and and the like it may help you narrow in on what is best for you. This is not a one size fits all situation.