Can't go wrong with either Atmasphere or Joule. I'd say
that the Joules are a slight bit more rich in the midrange, the Atmas are a little faster and have slightly more extension on top. That is not to say the Atmaspheres are lean. It is very apples to apples, imaging depth and spacial dileneation maybe go to the Joules, but other attributes will fall into the Atma camp. With both brands, the higher you go up in power, the more relaxed and accurate the presentation.
Basically they are both excellent amplifiers- you simply can't go wrong with either. I love OTL's, but your results
with both brands will vary depending on the speakers you're using.