"Best" is rather subjective.
"Best", meaning greatest potential size audience? Ebay.
"Best", meaning least shipping hassle? Local Autotrader or swap meet.
"Best", meaning a free listing? Craigslist.
"Best", meaning highest concentration of Norton nuts? Here.
"Best", meaning highest selling price? Your guess is as good as mine. Any and all of the above?
Prices for non-complete bikes have never been good, and prices for complete, perfectly restored bikes have fallen through the floor, so don't get your hopes up. Probably "best" to just fix it up and ride it!