I use either my 7' 3-wt or my 8 1/2' 4-wt, depending on the wind. The fly that I have caught the most crappie on is the venerable woolly bugger, either in olive or black. The other fly that they love is a clouser.
Several years ago when I used to fish Caddo Lake in East Texas, I was fishing exclusively with conehead woolly buggers and catching 15-25 crappie that averaged 1.5# each time I went there. There were several jig fishermen who weren't catching hardly anything while I was tearing them up. The reason I caught so many was because I was working the bugger slowly, while the jig fishermen had to reel in quickly to keep the fly from tangling in the underwater vegetation. If they had any sense they would have put their jig about 2' under a bobber and worked it in slowly. I was secretly laughing at them.