Originally Posted by Canada_Rockies 
The 50mm would be of more use for someone photographing inanimate objects - stamps, jewelry, etc. The depth of field is roughly double at the same magnification and aperture, and the perspective is different as well.
The 100mm is a better choice for taking pictures of creepy crawly things that fly away when you get too close.
The FA* 200mm f/4 Macro would be even better, but my wife won't let me mortgage the house to buy one.
That's what everyone says but I'm leaning to the opposite direction. DOF on 100mm is WAY too thin even at f/16 and stopping down further (at least on my lens) starts to lose sharpness. Before I had my 100mm macro I took some great shots of bugs using a reversed 50mm which required slamming the lens on the face of the bug (roughly 20mm focusing distance).