I had some blackjacks and bluebill the other day, didnt taste any different than mallards and gadwall to me. I like how they cook better on the grill though because they are a thinner piece of meat.
What I do with duck breasts is I will soak them in salt water for atleast 24 hours (after I have cleaned them thourghly) Then after the 24 hours I will marinade them in Italian dressing and beer, sometimes a little worshtitshire (sp? lol) sauce as well. For about another 24 hours, then I just BBQ them, some dont take as long to cook as others so you just have to keep watching them. Dont over cook them, leave them quite rare and they wont taste bad, and they will be much more moist.
You can tenderize them also if you would like to.
Ducks are like flying steaks, its all about how you cook them.