Firstly, if you are going to want to milk them, make sure that you can milk before getting goats. Its not as easy as it looks, and there is a knack!! Get in touch with a local goat owner, and ask if they can show you how to milk, etc. most people are more than happy to help a newbie.
Pygmy goats are not for milking, so avoid those if its milk you want them for. Sanaans, alpines, toggenberg, and the golden guernsey, plus the Anglo Nubian are all milking breeds. Angora goats are the ones used for their fleece.
Really, you want one in milk now, and then another in kid, to provide milk for next year, otherwise, if you have two milking, you will find you end up them both drying up and no milk at all.