I use eBay to sell my used gadgets, usually 1-2 months after I buy them, when I realize they actually won't make my life so much better.

And then I buy more gadgets. And so the cycle continues :)  

Not sure which one is better, I use eBay because I am familiar with it, and never bothered to make the switch to anything else - I guess it's because I am very happy with it, so there is no reason to switch...

I'll be watching this thread though, maybe I'll find a reason to switch!