I have found most fluorocarbon brands have very similar line diameters. I have never used fluoro for crappie but I do for trout. My preference in the 2-4lb range is Seaguar InvizX or Sunline FC Sniper. Sunline FC Sniper has a 3lb line I absolutely love. This line has no memory. It handles like 2lb but gives the strength closer to 4lb. Given crappie are not "line sensitive" I recommend giving a look at PLine CX Premium. It a fluoro coated copolymer line. It has the same diameter as fluoro. The cost is a fraction of fluoro.