Why not have both? They are very different and variety is always good.
A well bred Pekin will grow just as fast as a Cornish Cross and not have any health problems, as well as being reproducible.
I like duck meat. It is all dark meat and very rich. Duck is particularly suitable for oriental recipes. I've not had a tough duck yet, nor a duck that tastes like liver. But, if you don't like duck, then don't raise duck.
I think there is actually more meat on that Cornish Cross chicken, because of the over-size breast meat. On the other hand, I think that the ducks are more pleasant to be around. Which, unfortunately, makes them harder to kill because it is easy to get attached to them.