O Scale. O scale is 1:48 in the US, you will find a few variations around the world. When you think of O Scale trains, you naturally think of the classics like Lionel, American Flyer, Marx but there is so much more available.
O Scale can be quite collectible as well. As mentioned earlier, these trains were typically played with hard for years so finding pristine pieces can be a challenge. If you remember the Adams Family, Gomez routinely crashed and blew up his trains. I am sure many young ones enjoyed doing the same.