If you really mean "best" as in "price is not a consideration", then you should be looking at a device such as this:
http://www.imageaccess.de/?page=Scan...V2Professional
This is the type of device that professional scanning bureaux use.
If price is a consideration, and you can destroy the books, then a scanner with an automated sheet feeder is probably what you want to be looking at. Something like this:
http://www.amazon.co.uk/Fujitsu-Scan.../dp/B001VGJ7JM