I like to have a book for my specific bullet, a few generic books, and data from my specific powder manufacturers too. The One Book/One Caliber books from LoadbooksUSA are good resources.
One disadvantage of owning loadbooks - if you own just a few cartridges, you spend a lot of money on a lot of pages which you don't need. Then once you find your specific load which runs well in your rifle, you may not ever again need to open the books.
I have Berger, Speer, Sierra, Nosler, and Hornady bullet books, plus Lyman and Lee generic books, as well as the One Caliber/One Book manuals for about 8 or 9 cartridges (some books I have in multiple editions). Then I have data from Alliant and Hodgdon (online) for powders which they provide for free upon request, as well as leveraging handloads.com, loaddata.com, handloader magazine, etc etc online data.
Most important, to me at least, is to get a book with good process instructional tutorials. Load data is great, but if you're just starting out, having a line by line tutorial is worth a lot more than data.