You will as many answers as there are breeds. Figure out what you want ducks for first.
Meat, eggs, entertainment?
Then how much space do you have?
What are your local laws for keeping them?
Then do you have a color preference?
Do you have a size preference?
What do you live, what is your climate like?
Visit Metzer website and use the comparison chart. We have Khaki Campbell's, they are excellent foragers and high egg producers. They are smaller than say Welsh or Silver Appleyards and Rouens. Not as small as call ducks or other bantams.
Easy to grow out, easy to herd in at night. Not as flighty as runner ducks.
My runners are not skittery, and I think it is because I had the luxury of plenty of time to spend with them as they grew up. They are sweet and friendly, and love eating slugs and weeds and many garden pests.
It looks to me like they have knocked the slug population down by about 80% since they arrived two years ago.
They are a small breed, about 4 pounds, tall and slender, full of personality, great layers. I keep them above 40F, as mine do not thrive colder than that.
A friend has Khaki Campbells that she really likes. My two buffs, which I just got five months ago, are also good layers and decent foragers.
The Rouen drake is the the best looking of all breeds I have raised,but they grow quite big... up to 10 lbs. They look like a mallard but 3 times the size and are too heavy to fly. I also like the smaller breed runners which grow to only 3 1/2 lbs and have a neat semi erect walk. Runners are also good layers. Almost as good as the khaki cambells but several pounds smaller. Some like call ducks which are a cute small breed.Runners and call ducks come in a wide rage of colors. Another small breed is wild mallards ; beautiful birds but they are small enough to fly and probably will fly away
unless their wings are clipped.. something I would,t want to do.