Line is where every setup starts, and the three types, braid, monofilament and fluorocarbon, each have a distinct personality. Most modern setups use a braided main line and a fluorocarbon leader, but knowing why, and when to break the rule, makes you a better angler.
Braid
Braided line is incredibly thin for its strength and has almost no stretch. The thin diameter means more line on the spool and longer casts; the lack of stretch gives you unbeatable sensitivity and hooksetting power at distance. The downsides: it is visible, has no abrasion resistance on its own, and is slick (tie the right knots). Braid is the default main line for most spinning, jigging and surf setups.
Monofilament
Mono stretches, floats, and is cheap and forgiving. The stretch acts as a shock absorber (good for treble-hooked lures and hard-charging fish) and the buoyancy suits topwater. It is easy to tie and handle. The downsides: it is thicker, less sensitive, and it weakens with age and sun. Mono still shines as a shock leader, for topwater, and for beginners.
Fluorocarbon
Fluoro is nearly invisible underwater, abrasion-resistant, and it sinks. That low visibility and toughness make it the standard leader material, tied to a braid main line. It is stiffer and pricier than mono, so most anglers use it in short leader lengths rather than filling a whole spool.
Tip Think braid for the reel, fluoro for the leader. A braided main line for distance and sensitivity, joined to a fluorocarbon leader for invisibility and abrasion resistance, covers the vast majority of Northeast fishing; connect the two with an FG knot.