Fein Multimaster is state of the art for straight cuts.
For circular cuts there are some tungsten carbide hole saws specifically designed for rough cutting exterior walls. These are NOT the ones used to knock-out sheet metal. They have a gritty, ultra rough, abrasive style edge. It permits attack on stucco and brick.
Normally pitched to plumbers, IIRC they are imported from Denmark. I just can't remember the band name.
Skip the air powered tools. Just too much trouble to set up for field work. They suck down energy -- meaning that you need 25Amps at 240V to keep up with your tempo. Most of that energy is lost in compression and expansion.
