There are many different types of brake lathes on the market today. There are many different manufacturers as well a many varying degrees of quality and usefulness.
Most likely, if you are in the market for a brake lathe, then you are fairly mechanically inclined. Therefore, you probably already have a semblence of common sense when dealing with used machinery. That usually makes things easier, though not always. If you consider yourself to be "mechanically challened", keep reading; I'll try and help clarify a few things..
Anyway, on with the show....
The reasons that I like Ammco are fairly straight forward:
1.) They're common and have been around for years (parts and repair services are easy to find)
2.) They're well built (it takes some serious work to really screw one up)
3.) They hold their value
4.) Cones and accessories from other brands can be used on an Ammco machine.
The (3) different models (3000, 4000, and 7000) that I have listed are all different from each other, but many of the parts interchange.
The 3000 is a drum only machine. You CAN'T turn rotors on this machine.
The 4000 is a drum / disc machine. You can turn both rotors and drums on this machine.
The 7000 is a disc only machine. You CAN'T turn drums on this machine.
The 4000 is a good all-around machine, and is the most common of the three. With a properly equipped 4000, you can turn nearly any car or light truck drum or rotor. And if you want to turn medium to large truck stuff, then you can buy extensions, heavy duty arbors, etc.. to expand your coverage.
Also, with the right tooling, you can turn automotive and truck flywheels.