A quick search revealed many threads just for this.... like this one
http://www.crappie.com/crappie/main-...um/54043-line/
But, quick answer is whatever is on sale. Most all modern lines now are perfectly fine. Keep it fresh and keep it clean. I use P-line, Yo-Zuri hybrid, Stren, and others. 4# or 6# depending on the chance of snags in the area I'm fishing, and then tipped with 2# or 4# leader.
-Alexander
My candle burns at both ends; it will not last the night. But ah my foes, and oh my friends - it gives a lovely light.