All of the sites you've mentioned are fine. As with any car buying, it's the details and the spec your after that will determine the length of your search and where you ultimately buy from.
The a few positive points about buying from a forum member is that you can see (if your lucky) the cars history through the owners posts, re a build thread, and generally being a forum member will mean the owners an enthusiast so the car may have been maintained above and beyond the required amount with the latest revision of certain parts etc.
Pretty sure there's a few Eddy's for sale ATM on here.
Harry hunting!