Grip length, or overall height, is the most important factor for me. After that, width, then overall length, then weight. My reasoning is this: in a decent holster, the only thing that can "print" on your covering garment is the grip. The longer and wider the grip, the more it will print. Overall length is only important in OWB holsters, but most of my covering garments will conceal an OWB holster for a P226 as well as for a PM9...
Regards,
Kevin