Personally, with it just being my wife and I, I throw a lot of fish back. If I'm catching for just us I only keep around 7-8. If I take a buddy, I'll let them take all the fish with them, but try to encourage releasing females once we catch 10-12.
As far as size of fish to release, I feel its a bit of a wash. The average crappie lives 7-8 years and it takes around 5 years for a crappie to get to 12+". In return an 8" fish is usually around 2 years old. If you toss a 12+" female back she may only have 2 years left to lay eggs and she can carry more eggs. But the 8" female could have 5-6 years left for laying.
For the regulatory side of it. I'd like to see the size bumped up to 9-10" to help with the age structure in the lakes. I would also like to see the limit drop by 5 fish for sustaining the resource. Just my
Ankona Cayenne Kevlar, Suzuki 60