I got no idea I'm afraid.  Mine are all girls and they were mean to the littlest one to begin with but they're quite nice to her now.  Our neighbour insisted we didn't get any boys and she was so distressed about it that the guy who gave us them for free jus gave us girls.  I have to say, they're just gettin old enough to be needing a boy duck right now.  I feel kinda bad about it cos they sendin out all the boy attractin duck signals but no boy's comin along.  Maybe they'll get lucky and a wild duck will come land for a day!  
Sooo I would say, (but this is comin from a new duck owner who has only known her 3 girls, so see what other people think) that two girls and a boy would be good.  Our distressed neighbour however had that combination (don't know what breed) and it didn't work.  Meanwhile there's a guy on the forum called Peter who has two little ducks, he's not sure the sex just yet who are REALLY not getting along.  Maybe it's hit and miss.  Maybe we're lucky!! 
But, you will loooove them, ours are little chubby cheeek angels and very friendly.  Mr. Snoogles couldn't be bothered to make the jump to get into the paddlin pool the other day and stood there quackin at me until I picked him up and put him in.  They like being held and they come knockin on the back door for attention alllll the time.  We only got them cos their breeder had too many and had to get rid of them but now I love them to tiny bits.
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