I have decaled a lot of models over the years. Big picture, mostly I have used Champion decals, initially purchased from them directly before they went out of business, and later a good stock was obtained in a couple lot purchases. I also have some vintage Walthers and Scale-Craft decals. Of the three, Champ decals work well but the Walthers and S-C ones tend to look maybe a little better on OO cars, the lettering is a bit “heavier” and closer to OO (Walthers was the actual manufacturer of late S-C decals, more here).
It was completed more than a year and a half ago! (More here).
Then recently it was posted on the Facebook American OO Scale Railroading group that Tichy would supply their decals scaled to American OO. These are a game changer!
Their decals are applied a little differently than others I have used. I followed their directions exactly (found in the printed version of the decal catalog, included with my order) and used Solvaset as recommended. On some vintage decals Solvaset is dangerous, they break apart, so I normally use more gentle Microscale products. In this case, the Tichy decals went on beautifully with Solvaset! No bubbles to poke, on perfectly the first time. That alone is a huge time saver. I probably need to adjust my normal way of applying decals.
They have a large line of decals. The website listings seemed small at first, but do some searches and the size of the line will become apparent. They sell a lot of decals suited to OO models (especially roads in the eastern half of the USA), and print them on demand. I also purchased in my first order several sets of PFE reefer decals I will try as soon as I get some cars painted.
The way to buy them is to contact the owner via the contact page in their website. He will quote you the price (a bit higher than HO decals would be, and there is a minimum order) and I found the service to be quite quick. Website: https://www.tichytraingroup.com/
Again, for me, these are a game changer and do check them out. Even if you are a Lionel collector there are decals that closely match those seen on Lionel cars, you can do some very interesting (and prototypically accurate) restorations with these decals.
[Adding the note that, in spite of the April 1 date of the post, it is not April Fool's, these are a real product!]