Below are the breeds with which I have personal experience, meaning I have owned them, in numbers ranging from a two Lamanchas and their kids to several Mini-Manchas and their kids.
Oberhasli - Smaller goats, though still standard sized. Milkfat runs low to high three percents. Very quiet, gentle, friendly.
Nigerian Dwarfs - Very small goats. Reasonably quiet, gentle, friendly. Very rich milk, around six percent butterfat average. Milking ability varies wildly among individual animals, ranging from the doe with tiny teats, no letdown response and short lactations that gives 1/2 cup per milking, dries off at three months and is horrible on the milkstand, to the doe with a nice udder and teats, terrific letdown response, stands like a rock on the milkstand, has a lactation that ends when you make an effort to dry her off, and peaks at 5 or six pounds per day with a very gradual decline. Even with good bloodlines, you can't count on wonderful milking characteristics in an individual animal unless you see them for yourself, or you are buying from a person who has milked the animal on a regular basis and who's word you trust.
Lamanchas - Bigger than Oberhasli, if from show lines. Reasonably quiet, gentle, friendly, but I've never seen other goats ram each other the way I've seen Lamanchas do. Fine with people. Good quantities of fairly rich milk - percentages run from high threes to high fives.
Nubians - Large goats. Loud. Smaller amounts of rich milk. Somewhat richer than Lamanchas in general, but not as rich as Nigerians. Loud. Pretty and sweet. Loud. My first goats were Nubians. Gorgeous, sweet, fun. We named one of them Banshee. My good friend had a nationally prominent Nubian herd for many years. I loved visiting with her animals, and would have brought one home if I hadn't been living in town where a quiet animal was of paramount importance.
I personally keep
Mini-Manchas and have been highly satisfied with the milking characteristics and personalities. Others have been less satisfied with their Mini-Manchas. Since the breed is still under development, and different breeders are working with different goals (for example breeding for small size with no ears as opposed to breeding for good milking charactersitics), milking characteristics can vary widely, so it's a good idea to closely examine parentage before purchasing.