Lyman has one of the best 'how to' sections, lots of images and explained very clearly. It's the one I'd hand to a new reloader, no question.
Lyman load data is a bit hit n' miss. Some of it's been kicking around since the 30's without update--few new powders, new bullets, etc. But they _do_ give accuracy information, which is helpful for clues about how to chase down a good load. They also include good cast bullet data for every cartridge. Velocities are 'optimistic' in many cases, but not nearly as bad as Hornady.
Lee data is compiled from all the 'free' sources, primarily powder manufacturers. With a little Google work you can get it all for free. Still, it's useful to have it all on hand for quick cross-referencing. I _always_ check my loads against Lee 2nd Ed just to see where they sit. As a general rule, the powder guys give hotter loads; it's in their best interest to sell you the powder that gives the best results.
Nosler's load data has great accuracy info; it tells you which charge was most accurate for each powder type, and which of these was overall the most accurate. It's only 'true' in their barrel and firearm, but it's a big help. The latest Nosler is quite good overall, and useful especially if you load a lot of their bullets.
The Hornady book is wildly overrated. Their load data is completely out to lunch compared to everybody else, at least in the last few editions. The one upside is that they do list many obscure cartridges that you've likely never heard of and will never encounter. Yay. At least they don't make you pay for a second book of ballistics tables anymore.
No experience with Barnes, or Speer, or Sierra, but I'll pick them up eventually--the more the better.
I love old sources too, from P.O. Ackley to O'Connor to old copies of Handloader, to early editions of Lyman. Some of this old stuff was juuuust on the safe side of a Kb, but it's always entertaining.