I don't know about the Hobart N50, but the A200 (20 qt) and the A120 (12 qt) both use differently geared transmissions. IOW, you change gear ratios, whereas with the Kitchenaid, you don't change gears, you just feed the motor more "juice". Neither the A120 nor the A200 mixers are for the occasional baker (unless you have lots of unused space). The 20 qt comes in a tall (floor standing) or short (counter top, if you will) version. I think the 12qt is only a counter top version. I use a dolly to move my a120 around. In my younger days, I could pick up an A200 and move it around, but I'd never try to lift it up on a counter without help.
The downside of buying a used Hobart is that 1) the price is high -- they hold their value and 2), you may need to have it serviced. They use a sealed gear transmission, but they need the grease changed over the years. If they haven't been run in a long time, they tend to leak a small amount of oil (seals dry out and/or shrink), which is really just separated grease, leaving you with the thicker gunk stuck in the tranny and nothing to lower the viscosity. The good news is that there's very little that goes wrong with them if you maintain them.
The great thing about most of the planetary mixers is that they have the hub and can attach accessories. While the KitchenAid has a cute little hub for adding little helper gadgets, the bigger hubs can take pelican heads and shred a buttload of cheese or slice a lot of veggies.
Cooks Country TV has been using KitchenAids on the shows I've seen, but I swear they say "commercial" instead of "professional" and I'm not sure they're even as small as 6 qt. Time to go google. Nope, Kitchenaid's site says 6qt. However, if you notice the dough hooks, they're not the standard "j" hook, but a reverse spiral, which helps keep the dough from climbing the hook. Now I want one... dangit. I have a Kitchenaid 5 qt already, but these just look pretty. Everything is stainless, no coatings and all that.