Do you prefer dominant or recessive white?
EDT: Leghorns are dominant white (I). Dominant white is a mutation of black. They use dominant white on a black background (E) to be completely white. Unfortunately, if you cross them with something that does not have a black background, such as partridge or duckwing, the third generation is going to have some members that are partridge or duckwing, and will only show the dominant white in the places where they usually have black.
Cochins are recessive white. Recessive white will not show up in the first cross unless both parents have it, because it's recessive. But if you cross two white parents that have the recessive white genes, their chicks will be white unto the hundreth generation.
EDT2: I see you already knew this. Sorry. I'll leave it for posterity, anyway.
