Nigerian dwarf goaties, and they are a small dairy breed. The breeder I am getting my doelings from especially focuses on milk production, both in quantity and nice, milkable teats. The milk is delicious, but definitely try fresh first. The store bought kind is awful, very 'goaty' tasting (if you know what a goat buck smells like, that is what store bought milk kinda tastes like, how they smell. Hard to describe!).
Goaties can't be kept alone, so if you eventually get milk goats, they should be kept in a pair at least. A solo goat is a very stressed out, noisy goat, since they are herd animals!