I notice you are from the UK. : ) Houdy from Texas!
I do not really know what kind of ducks you have there but I will tell you about mine. Currently I have 14 ducks, with more in the incubator. I started out with a Magpie x Pekin drake, Inky and a pair of White Calls that I hatched out. I feel madly inlove and then bought 8 more ducklings from a feedstore (TSC). Anywho the reason I have ducks is because they are sweet, goofy, and we would love to have some big duck eggs to use for baking, hatching, and such. It all kind of depends on what you are wanting from your ducks, if looking for meat I suggest a White Pekin, or a Rouen. If you are looking for eggs the Khaki Campbells and Indian Runners are the way to go. If you are looking for a good show bird, try Calls or Cayugas. I have mine both for pets and eggs so some of my ducks are egg layers, and others are just adorable pets. I have a White Pekin (Ping) and s/he is very sweet and loves to be held and is super chubby. Maybe I should rename her Tubby?? Or Butter Ball? LOL
Then I have two Khaki Campbells and a Runner for eggs, and then a Rouen and 3 Swedish ducklings, Two blue, and one black. If you were going for mainly just pets I would say the Swedish ducks would be a good way to go. My two blues are so very sweet and do not mind being handle at all. Another thing I noticed is my crested girl is alot sweeter than the other ducklings. I do not know if all crested are like this, but..
Best of luck on choosing a breed (by the by, I only named a few of the many breeds. There are alot of different breeds to choose from out there), and don't get addicted like so many before you.
~ Aspen