As a bit of a Tablet collector I have some pennies to throw in here.
For game prep nothing beats the power of the laptop. 6 PDFs open and searching a fast as I need. It might be clunkier, but power and tools are just that much above my other options.
At the table I prefer my Ipad. Big comfy screens, powerful enough to handle searches still, and can even manage those gorgeous but not printer friendly versions of PDFs. Screen cap monster stats and frequent tables and it is golden.
Other "books" at the table. My older ipad (gen 2), Kindle Fire HD (original, 7 inch I think) Samsung Tab E (work door "prizes" wife and I each have one) and even the Nook color in a pinch are all good for various secondary uses (leveling up, Traveller character gen, even managing a multi character suite (a summoner style superhero in M&M again screencap the stats and it's quick browsing)) When pushed The newer (2018) Ipad is my strongest tablet and works well every time. The Tab E, the older Ipad (gen 2), and the Kindle all function at about the same speed with a notable comment: the Ipad is slower than the Tab, but screen size really is much more convenient here. The TAb is also the "only" cell connected device which makes it useful (door prize was related to Sprint partnership I'm not gonna move service from the Tab until it's done crediting itself off my bill, then the new Ipad gets that sim card love)
Now all that brings up the fun story of acquisitions. I got real lucky when my daughter commandeered my old Gen 1 Ipad. So I started buzzing pawn shops to get an older Ipad for my uses wanting that size factor and trusting that Apple would be very hard to screw up enough to truly "break" and still sell to a pawn shop. I got the guy at my local place to give me 2 Gen 2's for 75 each. Now I can pass them around the table whenever needed.
So in conclusion 10 inch is king, stronger is better, and in a pinch brand names only matter in added peace of mind. Looking for an older more common device (i. e. old Ipads) can get you a great deal.
Good luck and happy gaming.