Loft is a far more important measure of quality than species. The higher the loft, the higher the quality of the down.
If goose down and duck down have the same loft, they are essentially the same quality. Both species of down can be sourced in low and high lofts.
There are two main differences between duck and goose down to consider. Duck down has a greater tendency to have an odour if exposed to moisture. This tendency is even higher for lower loft duck down. Duck down is also less expensive than goose down. It's important to us to offer duck down products as lower cost options, especially since they can be just as cozy, luxurious and long-lasting.
Read more about goose vs duck here.
Compare the species for all products at a glance here.