Hi, and welcome!
I'm not sure there's a "most used" book, but in addition to the Hodgdon's book, the Lyman books, the Hornady book, Lee's "Modern Reloading" and the books from Sierra and Speer are all popular. Most of these are updated periodically, and it's a good idea to get new ones whenever practical--recipes DO change from time to time. And new components are either available (like lead free bullets) or on their way (like more lead free primers) that will add to the "knowledge base."
Like Joe (J Miller), I get a LOT of my recipes from the little "booklets" the powder mfrs. publish.
The "big" books you've gotta get in hard copy as far as I know. The little "booklets" are generally available online. Old meets new...
Several of the online vendors usually have a good selection of books. I've used MidwayUSA and Graf's more than others, but they're just two of many good ones.
Rick C