OK,
Everybody has been wonderful, so far, in helping me narrow down my choices on scale, type of track and era. Here's the next question I have...
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As we always remind people, there is no "best" manufacturer which everyone can agree on. Each of us has his or her own preferences. Some love the results from craftsman kits, but others avoid them because of the high price. Many like kitbuilding, or kit-bashing, while others just want to run trains, and don't have any interest in building kits. And, the abundance of Transition Era structures won't help you at all if you're building a logging railroad in 1910.
I enjoy kitbuilding, personally. Last year, I put together a Branchline Trains "Weimer's Mill" kit, which I was very happy with, and had a lot of fun doing. For the price of that one kit, though, I could have had several different plastic structures instead.
I find the Walthers Cornerstone kits are a good compromise between cheap, mass-produced plastic buildings and wood craftsman kits. These kits have a lot of details, and still give you an opportunity to create your own unique structure with paint, decals and small features.
Another good option is the simpler "4 walls and a roof" kits by companies like City Classics and DPM. These really are intended as starting points. They require a bit more creativity just to make them presentable, but their essential simplicity and low cost give the model builder a lot of freedom to customize and create.
Sign up for the Walthers catalog. Every month, quite a few structures are on sale through them, both their own Cornerstone models and other manufacturers which they distribute. It's a good place to look both for bargains and for ideas.
It takes an iron man to play with a toy iron horse.
I would encourage you to look at barmillsmodels.com for some really nice HO scale buildings. Still, I think all manufacturers have their ups and downs. Maybe use the ones you like regardless of who made it?
I have to agree with those who say that there is no one best source. On my layout I have everything from 30-year-old buildings made of printed card stock to a scratch-built logging shed. I have plastic models from Walthers, Bachmann, Model Power, Kibri, Heljan, and Atlas. Basically, I look through the Walthers catalog until I find something that's close to what I want, and modify it as necessary. My only restriction is that I think Life-Like and IHC look a little too cheesy / toy-like.
As far as the best scenery maker out there, look in a mirror. Seriously, I use raw materials from WS, Scenic Express, and Noch, but I find that over the years, I buy fewer off the shelf products and make more of my own (I flatter myself that I can make a better rock face using sculptamold and a putty knife than I ever could get from a latex mold). My wife has some flowering plants in the cabbage family which make perfect tree armatures. I go out every fall and trim them off, then dry them and re-foliate them with WS clump foliage. I use the manufacturers I do because they're readily available at my LHS, not because they're any better. Experiment until you're happy. If it doesn't look right, do it over until it does.
Connecticut Valley Railroad A Branch of the New York, New Haven, and Hartford
"If you think you can do a thing or think you can't do a thing, you're right." -- Henry Ford