I only have experience with chickens, and quail, but quail eggs are very small, if delicious.  I have located a local farmer that has duck eggs for sale, and I expect to give them a try the next time I need eggs, to see for myself what I think of them.  They used to be a little more expensive, but since lately chicken eggs have become very expensive, I think duck eggs from a private farmer are actually less expensive than chicken eggs from stores.  I saw yesterday chicken eggs for $14/dozen in a local market, up more than $10/dozen from a few months ago.  IIRC, duck eggs were $6/dozen from the local farmer.  Hopefully they're still available, and at that same price.