I would say German would be the best but they will be silly money, if you are building your own rotary machine then i would look on ebay, i have had some really good motors from ebay and they don't cost the earth, also a very good range.
Apparently Maxon is the motor to use if you can afford them. They are Swiss so I guess they run like a Swiss watch?? They use them on Mars rovers [I can't post links yet so you'll have to wiki Maxon yourself] so I'm sure they'll work great on a tattoo machine. They use them in the Stigma machines. I culled this info off of this [I had a nice link here but I'll just have to tell you to go to the forum at a site called rotarytattoo dot com] site. I had another link to a particular forum post on the aforementioned site so look for a post called Maxon vs. Mabuchi By the way, the forum I'm referring to is not anything like this one. They are pretentious as to make you prove you are a professional tattooist or machine builder before you're even allowed to register. I'm an aspiring machine builder so i think I'm the kind of people they want to keep out.
If you didn't bother to read the links then Mabuchi is a cheaper alternative to the Maxon. I have also found some pretty cool leads on brushed RC motors from RC online stores. I think they would work great for rotaries. I would go for the ones with bearings rather than bushings and the brushed motors for "crawling" seem like they'd be the best. I'm no expert though.
Sorry about the hyperlink thing. I'll upgrade soon so I can do links properly.
you can try portescap, seriously good motors, but quite a hefty price tag. But maxon seem to be the cookie cutter. The 21600 is used in quite a few machines, including stigma's. I'll be converting my rotaries to maxons when I have the money!
Think we had a motor talk in another thread, the two most common motors used in some of the higher end rotary machines is Mabuchi & Maxon motors, The brushless ones cost more, but run smoother. They also make 6V motors and 12V motors some make 9 volt etc.. For tattooing you will mainly see the 12 volt motor in most. The reason why is just for the wide range of different speeds you can get with the 12 volt motors. Like that hildbrandt assissan I just ordered, I have it apart doing some testing on the motor now. I suspect the machine that was sent to me has a 6volt motor in it. Now the problem with the 6 volt motors is they do not have the widest range of speed availble to achieve a consistent soft hit.