Fireline:
Pros: Very smooth casting, tougher than hell, excellent feel, acts like monofilament except when slip-bobber fishing, good diameter/lb. test ration, doesn't float so your cranks run deeper.
Cons: Eventually the fibers separate, expensive, fades with age, but fading doesn't reduce strength
Spiderwire:
Pros: very limp, tougher than hell, excellent feel, good diameter/lb. test ratio, doesn't float
Cons: Line twist will kill you because it's so limp, just becomes a big knot, expensive, can't use it with slip bobbers, expensive, pain to tie knots with, expensive
All of my spinning reels have a spool with mono and a spool with Fireline, all baitcasters have Fireline, I use them for casting and trolling mainly. I like Fireline MUCH more than Spiderwire, I just think it fishes better in my opinion.
Selmer