I have never used YSL eyeshadows. I do own other stuff by YSL and love everything i got so far. However i do own Chanel quads. One of them i purchased it last summer and i hated it! The colors were gourgous but they did not last on my lids at all... I thought i was never going to buy any chanel shadows again, but i did and this time i had a better experience. Like somebody else said here, Chanel quads are hit or miss. I purchased a single shadow from Chanel and i was very impressed.
I do own Dior shadows and i like them a lot. No complains there so far. But my favorite eyeshadows of everything i own are MAC eyeshadows and Makeup Forever. They are awesome and they last a long time. Good luck and have fun with your purchases!