Fluorocarbon, because it has the same refractive properties as water, means it is less visible than standard mono. When the water is low and clear, it comes into its own. I wouldn't necessarily use it when the river is up and coloured, as the advantages of fluorocarbon are not utilised due to the situation.
Sufix is good and behaves like mono. Some fluorocarbons are stiffer, but then again that could be an advantage when using a certain style or rig.