It is usually a good idea to have your domains listed in as many places as you can, you never know where the right end user might find your name.
1. Afternic - Afternic is a must for anyone, one of the oldest (1999) and the best domain marketplaces out there. The great number of partner registrars (GD included) makes your domain visible in so many places across all the continents (if Fast Transfer is enabled). You don't have to forward your names to their rather crappy landing pages, just list and forget. Always add a BIN so you can get into the fast transfer program.
2. DAN - I'm amazed of how fast DAN managed to establish themselves as one of the best players in the industry. I guess hard work, innovation and great customer service eventually pays off. Beautiful landing pages, fast payments and the ability to easily setup monthly installments. Dan worked pretty well for me, I even had a couple of sales where the names been parked somewhere else so there is definitely traffic on their platform, not just direct type in. If they'll manage to launch their registrar side of the business, this will be a game changer.
3. Uniregistry - Great platform, very cool design. You'll have to park there if you're hoping to make any sales. They have brokers and you can obviously assign a lead to a broker if you think he might do better than you in closing a deal.
4. Sedo - Good old Sedo, frozen in time since 2001. Not much to say about them really. No sales if you don't point your names to their landers or spend some cash promoting an auction. However once you get a sale they are pretty good at sorting things out, you know german style.
5. GD Auctions - The place is probably 95% full of other domainers rather than end users so if you're looking to let your names go at reseller prices, be my guest.
6. Epik - Epik's landers are pretty much the best in the industry so far, you get lots of (SEO friendly) customization options. I don't know about the sale process since I haven't sold anything on Epik yet. Just recently I sold a name at Afternic which was Epik parked so it seems the buyer preferred to pay a bit extra at Afnic rather than clicking the BIN buton at Epik. However it seems that Epik is really fast when processing the deals and the support is great.
7. Domain Agents - Worth a try listing your names on their platform. Serious people, they just get in touch when your name has an offer, probably lowball you a bit first but they sell names. Why not.
8. Flippa - Not exactly what it used to be but still a platform with lots of web developers and potential end users that will buy if they see your name there.
9. Namejet - Used to be cool, now just dull imo. I guess all the problems they had in the last couple of years hit them a bit. Still a good place to offload some names, just make sure you understand that you'll get paid the following month.
10. Namepros Auctions - Good, friendly environment, probably the fastest way to liquidate your names.
11. NameLiquidate - The new startup from Epik, looks really good, nice and clean design with a sort of dutch-style auction system. I like it but I don't like the fact that names go down to $1. I personally believe that seller should be able to choose the bottom price from $1 to $9. This platform has a great potential if promoted right imo...
12. Dynadot / Namesilo / Namecheap marketplaces - These are all registrar-side marketplaces. I never used any of them so really have no idea how they work. Worth a try ...
13. Twitter & Linkedin - Yup, they do work if used right. Make sure you don't spam.
Probably the best setup imo:
1. Pick a landing page. Epik or Dan are the best choices. If you value your name under $5k just list a BIN otherwise go for make offer. Usually add a higher BIN as most likely end users will try to get your name for a lower amount. For example if you want to get $2,500 for a name just list it at $3,500 so you'll have a bit of room to negociate.
2. Once you picked your landing page, go list the name with Afternic and Sedo. Make sure your Afternic (and Sedo) BIN is higher than the landing page since their commission is higher. You can also choose any other platform from the list above if you think they'll work.
Hope this helps a bit