With Brandstack gone (but possibly coming back), the alternatives are:
Pays 100% to the designer.
Pays ?% to the designer. Designers can’t sign up. It is by invitation only.
Average quality (in my subjective opinion)
Pays 75% to the designer.
And the winner is: LogoGround!
There are many others, but these are the four that I think are worth mentioning.
The only downside of selling @ LogoGround is that about 9 out of 10 uploaded logos are declined. The focus is very much on quality. If you’re not an experienced designer, you might find StockLogos a less frustrating option.
Disclosure: As the founder of LogoGround I’m probably not very objective, but if it wasn’t my site I’d still choose it as the winner. It has many more features to help designers sell effectively, higher quality logos and it pays 100% of the sale over to the designer. It’s a no-brainer.