Generally, open-back headphones are better for mixing purposes. There are multiple reasons for this, you accumulate too much of the sub-region in closed-back and you don't hear the sound as clear, you get ear fatigue faster with closed, and the small subtle details of a sound stand out much more with open-backs. Some of the more expensive pairs are in the same class as expensive kickers.
Closed-back headphones are good for recording solo parts if you're playing an instrument or singing.
One thing that can't be ignored however is crowd noise. Open-back headphones do not fair well unless you are in an isolated environment where external sound won't interfere with your sound quality. For that reason, it's almost always better to wear closed-back headphones when playing a set. There's just too much crowd noise and you won't hear the subtle changes you look for when wearing open-backs to justify it.
Try leaving them on your head and uncup one from your ear.