Over the years we've done both pneumatics and motors.
We haven't had much luck with the pneumatics. The compressor barely squeeks out enough air to run an arm an entire match. To get enough air you have to add more cylinders, which adds more weight. The Kop pneumatic conectors are also unrelaible, which leads to leaks and the loss of more air.
Motors have their own problems: backdrive, breaker blow-outs, and (in the case of the Keyangs and windows) cracking plastic gears. However, electons don't tend to leak out, and the battery isn't part of the wight
So you don't have to worry about losing power.
Another major problem with pneumatics is that they are not linear. The actuators have only two positions -extended and contracted. Pnemuatics are not good at raising an arm precise amounts.