Radars predict pathing by computing speed and bearing, they can’t provide an accurate firing solution for a target that is constantly shifting its direction and speed. So to answer your question, a normal radar.
I’ve had much more luck recently taking that issue into account and spraying a pattern around the lead indicator. Just firing your entire burst in one spot ensures that if the plane makes any shift in direction or speed, you’re going to miss, while varying your aim ensures that at least part of the burst will hit.
You can usually guess where the variation will be by taking into account what the aircraft is doing. If it’s diving, aim more for the opposite side of the lead indicator. Opposite if they’re climbing. If their manuevering, add some up and down to your spray as well, and increase the variation forwards and back. And if it’s a manuevering helicopter, a nice wide spray all around the indicator is a decent bet.
Works more consistently with proxy, but I’ve also seen increased sucess with the Shilka using this technique.