I have 4 featherweights, all bought online and I'm happy with each of them. If you buy online be sure the seller knows how to properly pack a machine for shipment. If you google "how to ship a sewing machine" you will get the info. You can email this to the seller.
My machines range in age from 1940 to 1964 and include a tan and a white model. They all sew fine, straight stitches. There is some little difference in the sound (voice) of my machines. I've heard some people think the white (newest) machines aren't as good as the others but mine is every bit as good as the blacks and tans.
If I were to buy another and price was not a factor I would look for the best mechanical condition, best cosmetically, most complete with case and accessories and if there was a centennial machine I would snap it up.
There are some very good featherweight specialests selling on the web. They recondition, rate and guarentee the machines they sell. They also cost more.
Good luck with your Featherweight search. You will enjoy it.