The biggest problem with any such list is all the possibilities of differences in people's experiences with them. By that I mean I could order some coins from dealer X and have the greatest deals ever. Then someone else deals with the same dealer and gets taken really bad.
A list of great, good, OK, rotten dealers is really tuff since some start out great and start driffting towards horrible. Others may do just the opposite. So what and who were great yeseterday, may be the worst possble places today.
Not to long ago this subject came up about on like dealers. One was praised as fantastic by a few. For me that one was one of the worst I've even seen or known. As an example such differences makes it almost impossible to try recommending on line dealers.
Of course this same thing is true of stores, shopping malls, catalog sales, etc.