The seeming ideal hook size for bluegills flies is ~ #10. One size larger or smaller than that would be really good as well. I've caught 'em on much bigger, but at lower percentages. This general guideline will work for most sunfish species like Redears, Pumpkinseeds, Green Sunfish, etc. Having the hook within the last 1/2" of the fly seems important for bluegills, if the tail of the fly is too long, you'll miss many more strikes.

For crappies, the flies I use are usually 1.25"-2" long. Crappies can certainly fit larger flies in their mouths, but they seem to eat the smaller flies like candy. Again...usually #10-#6 hooks. I've caught crappies up to 14.5" on 1/80th oz microjigs fish under an indicator.