I have three projects in progress: small Roubo bench, mantle clock, and loft bed. The loft bed has a lot of mortise action. For the last two years I have almost exclusively used dowel loose tenons in fine projects, as opposed to the 'gross carpentry' I do in making yard furniture.
Each post of the bed has at least three mortises. I decided to try two hand methods and one electric to make the mortises. The initial mortises are for the bed rails so a consistent flat bottom is important; the sides need only be straight with no care for smoothness.
The first method was the traditional mortise chisel--I picked up a couple of vintage monsters from Patrick Leach. The mortise chisel went fairly well with the only drawback being the mortise needed to be wider than the chisel. I had a problem achieving a consistent flat bottom, even with the router plane being part of the clean up. I really liked how fast the mortise chisel plowed through the pine bed posts.
The second method was the garage hobbyist favorite mated pair of drill and chisel, though in this case the drill is a brace. This method was actually the slowest of all three, and I still had the same issue with a consistent flat bottom, but the router plane did a great job taking off the peaks.
The final method was a plunge router with an upcut spiral bit. The bit came from Rockler on special around Christmas 2010. The router method was certainly the fastest. Clean up after the router was easy with a sharp chisel and no need for a router plane. The trade off for time was a lot of dust and noise.
I don't have any conclusions as to which is better since I can see instances where one method has advantages over another.