I think everyone will give you a different answer to this question. My favorite breed are Muscovy for a few reasons.
*They are very quiet, they don't have the loud quack that other Mallard derived breeds have.
*They aren't as obsessed with water as other duck breeds I've had are. Don't get me wrong, if there are puddles, they are still going to dig around in them, but they aren't going to splash all the water out of the dishes/pool and dig to the center of the Earth just because it got kind of wet.
*They have been more friendly than the other breeds I've had.
Some down sides to them are:
* The drakes get very large and eat a lot. The hens stay pretty small though and aren't as big of pigs.
*They are a roosting duck and that can be a problem for some. The hens fly very well, the drakes have a harder time because of their size, but they can also fly a fair distance.
*All ducks in general poop, A LOT. It's wet, big, smelly, messy.
*Drakes, in general again, are very horny. They will try to breed any other poultry you have, and then can/and will injure or at the very least pull out feathers and stress the chickens out if they can't get away.
If you have space for them to free range you shouldn't have as much issue with the mess, or drakes trying to breed chickens. If they are going to be locked in a run, make sure you have enough space for the breed you end up with, and only get hens.
I have also had Pekins which I found to be huge bullies and wouldn't get again unless I was planning to butcher. Buff Ducks which I did also enjoy, they were just louder and messier than the Muscovies. Some call ducks which I loved, but they fly VERY well and need to be penned or have wings clipped. They are loud and messy, but in a smaller package. If your space is limited, they would be another to consider. Also had some East Indie ducks. They are also bantam like the calls, but they stayed very wild and also flew VERY well.
This turned a bit into rambling, but mostly make sure you are ready for the mess and noise, and make sure your space is adequate for the breed you get. You will enjoy them very much if you do!