Nice topic!
For many ubitx builders around the world, adding a simple audio derived AGC circuit is enough. Several excellent designs. ND6T has a version now sold assembled by N8DAH, or could be home assembled. Sunil offers another AGC circuit. I am using a third option based upon the VK3YE design that I am thrilled with. I slightly modded it, see K3PZN ubitx page for a description.
For many ubitx users, any of these simple AGC circuits provides something good and simple.
For more advanced builders, the HYCAS AGC by W7ZOI previously mentioned by Farhan is excellent. But its not an easy integration into the bidirectional amplifier for the average builder. (I built one of these but its waiting for use in a homebrew receiver).
Those doing the Jackal will get what should be a nice AGC that seems to be based upon the Hycas. Jack sent me the link to its schematic a while back.
If you want to add AGC,? enjoy whichever path you choose.
Curt
