I don't think there is a "best" year when it comes to Featherweights. Condition is probably the most important thing, but even then most any of them can be restored.
I have a black one and a green repaint, both are from 1936 or 37, I forget at the moment. I just love them both. I have been sewing on the black one a lot lately. It purrs like a kitten, so sweet.