I fish the local lake and a few small ponds with a good stock of bluegill, crappie, bass, and several other "panfish".
I tie 90% of my flies for those locations in size 12 or 14. Normally a pheasant tail nymph for sub-surface or a CDC caddis or Griffin's gnat for a dry will get action, but last year things really slowed down in late April & early May. I tied up a few buggy looking creations one evening just to use some new maribou & bead chain I had recently purchased. #14 hook, flame red maribou tail, body. & head, and fl chartreuse eyes.
Went to the lake the next evening and things were slow as usual. I tried the PT nymphs and got a couple fish, then decided to tie on one of my new creations. Fish after fish - on almost every cast! Almost all were 8" 'gills (big for that lake), but a few crappie and one fair sized bass (14-15") fell for that fly, too.
Took my son with me the next evening and we got the same results. We tried a few different patterns and only that maribou bug was working well.
That action lasted for a couple weeks on the lake (in a few different locations), then that pattern stopped working as the water warmed and I went back to dries.
I'd say for panfish drop down a couple hook sizes and go for "buggy" creations in various colors. Let the fish tell you what they're hungry for.
That fly I tied didn't produce much all the rest of last season, but you can bet as the water warms this year it will get tried again.