I say if you have any debt at all, sell. If you are debt-free, donate.
I did a lot of selling over the years, but we were struggling financially as well back then (probably from buying all that JUNK we didn't need ;) lol). When I reached the end of selling things (pared down to just a few suitcases of stuff left) I was so over selling. It had drained so much of my time and life. I can say every little bit adds up fast! I easily made several hundred dollars every yard sale and I hardly sold anything. You realize just how easily things of little value can cost you a lot of money as a buyer. You also learn new appreciation for the value and price of things when you have to sell things like that. Because you often can only get a quarter of what you paid, even if they are brand new. It just makes you become so much more careful about where and how you spend money in future. You really can make a lot from selling though, so if you need to get out of debt it is definitely worthwhile. Otherwise, it does suck a lot of time that in my opinion is probably not worth it. At one point it was like having a full time job for me, I was getting rid of so much so fast.
I donated a ton in the end anyway because we had so much left that didn't sell. I didn't want to have any more garage sales (hate them) and I came across this awesome concept shortly before I was done getting rid of things that says: GIVE FREELY, RECEIVE FREELY. It changed my perspective in a lot of ways. I always loved to give, but now it's like a way of living for me, an approach to life. I feel like if I give something out of real value that I would otherwise of wanted to get something for, I am making an even bigger sacrifice, but also making a bigger contribution to someone else's life. I love the feeling of giving to someone else who needs something when I really don't need it. It may have monetary value, but it doesn't have actual value to me. Also we love to shop at thrift stores so I feel like that is good as well since you are providing clothes and such for other people in need, whilst they are providing the same for you when you are in need. I don't necessarily believe in Karma but I do believe in many ways, you get what you give in life. And that doesn't apply to only 'stuff'. I apply the give freely concept to all areas of my life.
Good luck with it all! :)