Depends on what you want to do with the tractor. If you have a small piece of land and you want to farm a garden then a Farmall Cub is a great choice. They are cheap, lots of spare parts, and loads of really neat implements that can found and purchased cheaply. I like Fast Hitch implements which are harder to find and more expensive.
The most useful Letter series Farmall is a C or Super C. Install a Fast Hitch (yes it will also fit a C) and you have a very useful inexpensive tractor. My favorite. I love the M and H too, but you can't put a Fast Hitch on either one so you are limited to pull behind implements.
Just my 2 cents worth.
C&O2-10-4
