What is the right way to strip power wires?
This is the stripper I use:



It's got cutouts for 14-2 and 12-2 NM cable sheathing and inner conductors, and a decent set of sharp bypass cutters near the hinge for cutting wire.  It works better than anything else I've used for 14-2 and 12-2 Romex -- just squeeze, give it a little wiggle for good measure, and the sheathing pulls right off.  It's almost impossible to nick the conductor insulation inside.  For 3-way wire it's not so foolproof -- I use the cutter blades close to the hinge to score around the sheathing and then pull it apart.  Probably as good as any other method and is still faster than doing it manually with a knife.  

They also make a 12/10 gauge version and possibly others.  I got mine at Lowe's.