Ideally, you only want to breed two perfect birds together. Unfortunately, there is no suh thing as a single perfect bird, much less two of opposite gender.
To a certain extent, the previous two posts make some sense.
One thing that no one has yet mentioned is the difficulty in correcting the DQ. Some DQs are easy to breed out. They may keep cropping up on occasion, but if the majority of the offspring are unlikely to inherit it, using a bird with a DQ is worth considering if you have no other bird available. However, some DQs take many generations to get rid of.
For example, on a cross between a black skinned, mulberry combed bird and one without the FM gene, most of the offspring will end up with dark skin and dark comb. A few end up with light skin and red comb. And occasionally you will have one who is dark skinned with a red comb. When you already have dark skin, getting rid of the red comb is VERY difficult.
On the other hand, if you have a single combed bird who is stuffing in every other way, breeding him or her to a correctly combed bird will give at least 50% correctly combed offspring. If the correctly combed bird is pure for the correct comb genes, then all offspring will have correct combs. The thing you will need to remember though is that the correctly combed offspring in either case only have one set of correct comb genes, the other set will give single combs. (It is actually a bit more complicated as there are several genes for comb type.) So you need to remove the wrong combed bird from the gene pool after the first cross, and you want to mate the offspring back to the correctly combed parent or to an unrelated bird. Breeding brother to sister will give you a percentage of birds with incorrect combs.
In general, a bird who is outstanding in every way except for an easily corrected DQ is probably a better choice than one who is so-so, but has no DQs.