From purely a size perspective and without getting into the streamlined versions, I'd say there are at least 4 categories of Hudsons produced by Lionel. Others can chime in, but here's the 4 I've come up with:
1. Scale Sized - these include pre-war, post-war, and modern versions. As someone pointed out above, some might not be considered true scale models due to lack of detail, but there's a large group of from the various eras.
2. Lionmaster - New in the modern era. Not-to-scale, but more detailed than categories below. Might've only been a few offerings in this class in the 2000s (I love mine).
3. Baby Hudsons - This name, I think, was assigned to the ones like the 2046 and 2056 in the postwar period and some similar models, I think the 2065, etc. The O27 semi-scale Hudsons made by Williams and Williams by Bachmann in the modern era are similar in size.
4. Junior Hudsons - These are even smaller than the Baby Hudsons and were made in the modern era. You can find some of these on the Lionel website.
