I used to be the set up man for a tractor and implement co. That means, I assembled the stuff. The cheaper cubs, at that time, were yellow MTDs. The expensive ones were as good as anyone made, but the cheap ones were about the same as anything you can buy at Lowes. Not to say they're not worth the money. One thing I checked on when I bought a new mower was the transaxle gears. A lot of them are plastic. You can look at the transaxle and get names, spicer etc, and numbers, and find out which are plastic or metal. BTW, I bought a huskee, a tractor supply brand.
The VAST majority of common market lawn tractors are MTD made. Most of the lowest end machines (Murray, Huskee, Yard-Man, White, Craftsman, Yard-Machines, and many others) are all or have been made by MTD.
The difference is often in the minor details and features. And I too have heard of plastic gears in the transmissions - although I haven't seen them myself.
The Cub Cadet name has been bought and sold so many times, it's hard to keep up with who really owns and makes them. My understanding is that they are currently on an upswing in quality - trying to get name credability back.
As I said - between the Cub and the Craftsman - there's not $10 worth of difference - so the Cub would win my money if I were choosing between those two models.