Down is a natural product, so fill quality, odour and durability can vary quite markedly within a species depending on the breed, age and condition of the bird.
Practical performance is also strongly dependent on the skill of the processor and the quality of any proofing applied.
These sources of variation are greater than any variation between duck and goose down, so in practical terms duck and goose down of equivalent fill-power should perform similarly, provided they both come from a reputable supplier.
Philip Werner at SectionHiker.com reviews a lot of gear. Here's his take:
The down fill power test doesn’t care if the down being measured is duck down or goose down and the manufacturers I talk to think that 800 duck down provides the same insulating power as 800 goose down. I agree based on my experience using the products. You can’t tell the difference. Even more so if they’ve been treated with a water-proofing technology. I think there’s a lot of emotional baggage that people carry when they insist there’s a difference.
However high quality duck down is quite rare. The best quality down is harvested from mature birds, and ducks are normally slaughtered at too young an age. I think that the prevalence of goose down in the higher quality outdoor products is more a factor of its wider availability rather than any inherent technical superiority.
If you have any doubts about the potential of duck down, just recall that the very best down of all is Eiderdown (though this is academic for most of us as the cost is eye-watering).
The best source I have found is from Nemo