Zremesher

Zremesher is a script in zbrush that will automatically retopologice your entire mesh. I don't trust this script because sometimes its edge flow can be very funny. You can control the script to some degree like guiding the edge flow and show its poly density. The test mesh I'm using is a model I made in Maya

Dynamesh version 

Zremesh with no guides. The scripts processing time ranges from 15 seconds to 1 minute. Processing time depends on the poly budget you give it.

Here I have drawn on zremeshguides for the script to use as a guide for edge flow. The blue and red highlights are painted on the mesh. These highlights indicate poly density.

Red = X2 polys

Blue = X0.25 Polys

White = X1 Polys

Overall for this test the edge flow didn't come out bad but there are some areas I see were it can be allot better. I feel it would be more safer to do retopo work more manually. But depending on what is required I guess I'd only use it 10% of the time.