Kindle Fire HD 8.9, google nexus 7, Ipad for etexbooks

So I am headed off to college this year and I really need some advice on two things. One, as far as reading textbooks goes what is the ideal sized tablet for the job. And two whats the tablet that runs the etextbooks the smoothest. Additionally it would be nice if the tablet gave me the best bang for my buck because right now through amazon student the kindle fire hd 8.9 would only cost me 200, the nexus 7 would cost the usual 230 for me, and through a friend I could buy an iPad 4 refurb for around 360. All prices obviously in USD. Thanks in advance for the help!