I don't think there's a one "BEST".
I tend to stick with the published data from the manufacture of the "Bullet" I'm loading for.
That said, for cast stuff I use the Lyman Cast manual.
For various pistol and rifle loads, I use Speer, Sierra, Hornady and Nosler manuals specific to the bullet I'm shooting. Layout of the manual, and the balistic charts in the back, with the two piece pistol/rifle set, I prefer the design of the Sierra manuals.
Remember though, that if you're shooting Rainier LSWC, there won't be reload data in the manuals listed above particular to that bullet. And the Speer and Hornady are the only two that list LSWC load data since Sierra and Nosler only manufacture jacketed bullets.
My next step will probably be to a Balistics software package.
-Steve