Between a pneumatic die grinder:
and an electric rotary tool:
What are the advantage/disadvantage between using each one?
Also, which has more torque?
Pneumatic may be lighter weight, but you need a compressor that can keep up with it, and the exhaust airmay be a good or bad thing depending on what you're doing. On the other hand, compressors have other uses too.
A third option would be a flex-shaft tool.
Before buying any of them, know what you're going to do with it. Unless you have a specific task you need it for, you might be better advised to invest in a completely different kind of tool.
pneumatic tools can run for days and never get hot, but the compressor gets hot. from a power consumption perspective, electric is much more efficient. pneumatics have to be oiled regularly and create condensate issues with water in the discharge exhaust. pneumatic is really just an old technology that is becoming more and more obsolete all the time. still great for painting, but electric is pretty much better in every way. for a cnc, you can get water jacketed motors that run high speed and torque for hours at a time.