First you need to think about what you want to do with probably about a gallon of milk per day per goat, once any kids are weaned.... also do you just want milk or do you want breed pedigree goats (and register them). Buying a registered, and preferably milk-recorded goat (or her offspring) is really the only guarantee you have for a decent milk supply. If you want to make good cheese a good butterfat content is a must, AN's are probably more reliably good at producing fats of above 5% - they are also very noisy and they are big/chunky goats.
As to breed everyone has a favourite breed, and would champion it above all others...but most goatkeepers I know have at least two breeds, if not more...
I think the goat world is the only one that allows the registration/showing of crosses on an equal footing to pure-bred animals, so don't disregard them, especially if they come from good parents.
Also look into horned vs disbudded, decide which one to keep and stick to it. If you buy registered stock they will almost certainly be disbudded. Make sure you know what males are available within the distance you would be prepared to travel (at less than a day's notice) - I travel about 300miles round-trip to get some of mine mated, but I try to line-breed. You will need a livestock trailer or a van to transport your girls.
Also find a "goat-friendly" and "goat-knowledgable" vet before you get your goats, if not get a good goat veterinary book straight away too.
The BGS website has info on all the breeds, and there will be some at an agricultural show near you - talk to goatkeepers there. We are very talkative about our darlings!