It just depends. A lot is simply the individual bird, some just seem naturally friendlier than others. It also depends somewhat on how they are raised and how many are raised together. In general though, my Mini Appleyards are my friendliest ducks. They always seem to be the most outgoing in my flock even as ducklings.
As far as the other breeds, in general- my Anconas were friendly, my Dutch Hookbill was very calm and friendly (only had one though)....other breeds that have been pretty calm in my experience have been Swedish and Australian Spotteds. A lot really does depend on the individual birds though. Runners are generally known for being skittish, but I have some that are extremely friendly as well.