Personality and evenness of lactation. I like Nubians, have one purebred, but she sure is a character. Lactation is fairly even but does drop off some midway. This is of course genetic, but tends to be a bit more common than with Lamanchas. I also like the thought of having an "American" goat breed. We don't have an extensive history of domesticated landrace types like Europe does, but Lamanchas are a close second. An F1 cross will usually still milk out 7-8 lb/day for me. ~4.6-5% BF, 3.8-4.5% protein (varies).
One other thing is that I have noticed Nubian milk to be "too" good for cheesemaking. The calcium structure is too strong due to the high solids and micelle size. In hard cheeses, unless you take measures such as overnight pre-acidification, or prolonging the pH curve lag in some other ways to solubilize the casein, it will give the wrong kind of minerality. Not chalky, more drying in the mouth and hard on the teeth when you bite down.