Unfortunately, I have very weird dark circles and all MAC concealer's turn my circles either green or ash grey, sometimes at my local MAC store they try to see if they manage to disguise them and always give up and conclude that I would have to customize my own concealer and blend it everyday. While I wouldn't bother doing it for someone I was applying makeup on, I certainly don't have the patience to do it for me.
My HG concealers are:
Makeup Forever's lift concealer in #2, not only does it brighten my dark circle area, it always has a lift factor to it that shows when I'm feeling more tired.
Then I add touches of light with YSL's Touche D'Eclat in #2 just in the inner corner and the brow bone to bring some light.
I usually don't need to set these with powder and they last a good 8 hours.
I'm a guy and it's very discreet, but if you look closely, you can see the circles, if I want a flawless look, I'll have to resort to foundation, which I tend to avoid because it gives me an unreal look. Still, does Select Tint counts as foundation? *grin*