I'm still kind of new to the world of "domaining" but i can tell you my personal experience.
i have sold 2 on ebay, and 2 on flippa, zero on SEDO.
What i don't like about SEDO, is that it seems like they threw 30 different websites together, and at first, it's very strange and unorderly to navigate. Flippa is much cleaner and more organized. With that said, the PRO people, who have 10k to 100k domain names don't use SEDO anymore. I have read numerous articles about how they rip you off, how they charge 20% commission, and how, on parking pages they take MOST of the ad revenue and give you .01 to .05 per click, whereas other places give you 1.00 or more per click. There are other reasons too, however, at MY stage of the game, with 100 domains, i'm not seeing a huge difference.
However, i also hate how SEDO's TOS says that you strictly CANNOT drive any sort of traffic, WHATSOEVER to your parked pages. Speaking of which, i'm trying to find a good alternative to that now.