I don't anything about Afternic parking because I've never used them. However Sedo doesn't have a stellar reputation for parking revenues, although Sedo Pro has some reasonable stats. For parking, I can recommend Parked. You should of course try several companies to evaluate them.
I get many more sales at Afternic than Sedo. I don't think those sales would be any better if the domain was parked at Afternic. Better communication from their sales reps/system generally too.