In my experience the best measure of a company is the support. And if you have the same person to talk to each time, its even better. I have that at Sedo, Godaddy, Moniker, and other places. I have not had any unresolved problems, so I am happy. I dont expect the world to be problem-free, but you want to see things get resolved in a timely manner, and the burden of communication is for all parties.
Godaddy is amazing how fast you get to a real person - though sometimes you have to escalate it. Godaddy has a front line of people but the harder stuff goes up a level to a more experienced group. So you sometimes have to push through some initial resistance... but professionally, of course.
Sedo is good. Not always fast enough, but no domain broker is fast, unless it is done by an individual acting as a broker. I like Sedo more than Afternic right now, thats for sure. I have no dedicated person at Afternic, and their listing software excludes some domains that are completely, 100% acceptable. Also, when adding domains to Afternic, it can take anywhere from a couple minutes to 10 minutes or more to respond to a list of 40 or 50 additions; but Sedo is fast.
I recently sold a domain at Sedo, and the buyer was lagging on completely the transfer, so Sedo moved the domain to their account so they could pay me; it was very good.
If you dont like Sedo, then pay twice the fee and use BuyDomains.
Kevin