Well I certainly agree that the Greeberg guides @ $100 each are certainly "THE" definitive guide to the era's covered by them. However, let me add a word for Doyle's " Collector's Guide to Prewar Lionel Trains 1900-1942" It covers 2 7/8 gauge, Trolleys, Standard, 0 gauge, and HO gauge as well as Catalogs, paper products and accessories. It is crammed full of pictures including illustrations of period advertising (far less text than the Greenberg books) and depends mostly on visual display. It is however of a simple "paperback" book size that I find easy to take to train shows etc whereas taking the Greenberg books is not possible. So like others, I am not sure there is ONE "best" book and to some extent it depends on what you want to use it for. I use Doyle as a quick reference and as something I can take to shows. I then use the more elaborate Greenberg guides to conduct more detailed research. By the way, the price of Doyle's was $19.95 new and I think I bought mine used for under $10.
Best Wishes and good luck
Don
