SEDO is believed the best one and trusted by many people over there. So I suppose that would be good idea to use that.
It really depends. If your domain is at namecheap, and you do not want much for it, add it to their marketplace. I have sold quite a few domains there. No fees, either to sell or buy.
Sedo is great but make sure you put a price and not 'offer'. The price range is too large there so buyers may be nervous to even submit a bid on a lower price domain.
Sedo is better.But you do have so many other choices too. Like Afternic,DNforum,buydomains..try find some
I prefer namecheap. It's all about personal preference and what you are looking for in terms of services offered. Some people like godaddy some people swear by hostgator.