I have a YM-2 and a YM-15. As far as I'm concerned, you can go wrong with Ambex. Although I haven't taken their roasting class, I've heard from others that it is great. What impresses me about the company is that the chiefs there have tons of education...you'd be dealing with some really smart guys.
Face it...most coffee roasters are built in Turkey to begin with. Once they arrive here, the gas burners, controls, etc., are added. So the quality of the components going in are of particular importance. Next is, of course, the knowledge and support of the company selling the roaster. So far I have not been able to stump these guys...they know the coffee business!
I always have a standing invitation to anyone who is willing to make the trek to north Georgia to come and try out my roasters. You're more than welcome to come give them a try!