Most concealers work well for covering minor blemishes, but finding one that covers dark circles is more of a challenge. Peachy concealers are suitable for counteracting the bluish and purplish undertones of dark circles, while pink concealers work best for those with grey undertones. Make sure you understand the undertone of your dark circles because pink concealers can accentuate the bluish undertones of dark circles (in color theory, pink + blue = purple).
MAC Pro Longwear concealer in NW20 and MUFE HD concealer in R30 work best for counteracting my dark circles. They both have a pink undertone, but it's not too strong where it would accentuate the bluish undertones of dark circles. They also can be worn alone without having to layer a yellow based concealer on top, even for those who have a warm complexion like myself. They are also one shade lighter than my skintone because I like the brightening effect. I just set it with a powder and they last all day without creasing or looking cakey. R22 has a stronger pink undertone and is lighter than R30. (For reference, I'm a MAC NC30/35, MUFE HD Y345, L'oreal True Match W4, and Dior Forever 021 mixed with 031.)
For those who find that peachy or pink concealers are still not enough to diminish the appearance of dark circles, then I recommend using color correctors. They are not concealers, and instead are intended to correct discoloration. Therefore, they must be used in conjunction with concealers.