What is the best knee brace to wear when someone has clicking in the knee along with instability and pain?

Open patellar sleeve. It sounds like you have some subtle dysfunction of your kneecap, aka patellofemoral joint. Start with a simple neoprene sleeve with an open patella. If you have tried that in the past, a j brace is similar but more robust. It uses a pad to improve the control of the patellar tracking. I hope that helps.