I've used both Williams and Lyman receiver sights on a wide variety of rifles and found them to be all good. But for personal aesthetic reasons I too would opt for the steel Lyman 66, especially on a lever gun made before the 50's.
I would add that the Lyman 56 is The Classic receiver sight of all time. I have several Williams on a couple of Marlin 1894's in .357 and they are excellent sights. I also like the Ashley XS sights originally developed by Ashley Emerson now known as XS Sight Systems. These are more modern but are really good.
