Cal CL-15
Right around $500 used. You can't beat it. Neither can any of the others listed. For this kind of money, depending on the rest of your system. You are as close to Hi-Fi as you can get. I use one in my system. I know it is the weakest link in my system. I always think about selling and upgrading.
But I am very happy the way it sounds. So I can't come up with a good enough reason to justify selling it.