I have 2 welsh harlequins and they are crazy aggressive with the neighbor's ducks. They have 2 pekins and 2 Rouens. Their ducks are sweet, calm ducks until mine show up. They get frantic and they all go at each other through the fence! My 2 started it as ducklings. WHs are a lightweight breed and mine  have no idea they are! Like piranhas! Or chihuahuas. Lol. WHa are also supposed to be more laid back and friendly. Ummmm, not mine! The female has never been really friendly, but the male is ok. They follow me around, but don't want to be touched or held. They're pretty, but really snotty. This is my 2. 
This is Tot the snot. She's the female. Their names are Tater and Tot. Pretty is as pretty does... Lol. They're good ducks, I'm just mad at them for being such butt heads to the neighbors. Not the usual WH. 
I love the neighbors pekins and Rouens. I vote for those breeds, BUT my #1 vote goes to a Muscovy! Sweet, quiet, very broody, friendly.... All of the traits you'd want. The only thing you have to get past is the red caruncles on their face/heads. The females can have very little if it's something that puts you off. If it does, I get it, it did me. Now, I'm hoping to get my neighbor's 2 new ones after we see how my drake is going to act once the hormones kick in. Hopefull the new babies are girls! Scovy personalities have won me over. Plus, they come in a TON of colors. This is the neighbor's new babies.