On most of my set ups, braid line as the main line then a fluorocarbon leader. I have one spinning reel spooled with 4 lb fluoro on my river rod that helped with landing a 22 lb chinny.
Over all, it does really depend on what your target species is and the conditions you think you will be encountering. Conditions such as water clarity, abrasive structure, temperature, etc.
In my limited fishing experience, fluoro tends to be more brittle when it gets cold. Mono does well, braid is good but builds up water to ice the guides more.