I carried my 5D Mark III with the 100mm f/2.8L IS macro lens. If I had to have only one lens and it had to be a prime lens I'd be stuck between a 50mm and a 100mm macro lens.
I'd probably end up choosing a good 50mm lens but when I bought a Minolta 9xi film camera after I had given up my manual focus Minolta X700 bodies, I bought it with a 100mm macro lens. Maybe someday there will be a 50-100mm f/2.8 macro lens with image stabilization.
Here are some of the results with exposure information.
|f/8, 1/45 sec., ISO 400|
|f/11, 1/60 sec., ISO 400|
|f/8, 1/125 sec., ISO 400|
|f/11, 1/180 sec., ISO 400|