I have the second book (Sease's) and borrowed the first (Bestor's) from my local library (love your library
) and I would say if you plan to travel with the book and don't necessarily want an extensive collection, just the down and dirty go with Bestor's book.
CO/BO 54 is more compact and has enough overlap with Sease's book to be useful for the beginner to intermediate knitter. However, if you want a little more in-depth gathering of cast ons and bind offs then go with the Sease book.
Both books are spiral bound so they lay flat, have color photographs of what the end result of the cast on or bind off should look like (although in Bestor's book both a frontal and flat view are shown), and have some form of grid or listing of what type of cast on is best suited for what purpose (e.g. all purpose, durable, elastic, etc.)
I will admit that in either case (photograph or drawing) if the process wasn't explained clearly I had to take a second or third read and or look to understand what was being done. Also both author's use cos/bos from knitting personalities
e.g. Cat Bordhi, Jane Pimlott (aka Tillybuddy), etc. so you may already be aware of more co or bo than you realize, that are in their respective books. I did like that Ms. Bestor has a resource listing at the back of her book and that she had little drawings at the beginning of each section showing which co and or bo could be used where (two of the reasons why I think a beginner might find this book helpful); however, I didn't like that she only showed two types of knots as a way to obtain a foundation stitch.
I also agree with knitcindy if you can borrow one or both from you library or browse
a local bookstore that would probably be the most helpful and objective route you could take. Sorry this is so wordy, hopefully you can find something useful in this hodgepodge of words.