I always sell on AdultDVDMarketplace.com. It's a piece of cake. They make suggestions on what you should price the DVDs, based on the cost on other sites. You can keep track of whether yours is the lowest listed or not. You can put the listings on hold if you are on vacation or something, so you don't have to cancel and relist them all. They will direct deposit your account balance into your checking account once a month, unless you have spent it on new purchases.
I always use adult dvd marketplace and I'll continue to do so.
You can use Ebay, but they have so many restrictions on how to list things, what words you can't use in descriptions for no apparent reason, they won't let you use their own rip-off paypal either... and Ebay buyers can be plenty of problems getting them to actually pay (and I've never actually went and sold porn there either)... but if you do get a listing up, people often seem willing to pay way too much... probably because they don't look around or are afraid of real adult movie vendors for whatever reason.
So, it has it's ups and downs selling on Ebay. Like I said, I recommend adult dvd marketplace.