i think given what your looking for id go with a lamancha, there the most easy going and typically "quietest" of the dairy goats, alot more puppy dog like. i LOVE nubians, but they tend to be drama queens and a little "needy" togs from what im told are the "jumpiest" of the group and tend to be a little on the skittesh side. ive met a few alpines and all were nice but a little "indifferent" to humans, they only cared to be around people if there was food involved...and im told the sannens tend to be similar...the lamanchas though are supposedly incredbly sweet, frinedly, good producers with a nice middle ground on the milk, good production nice for milk and yogurt/cheese.
a wether makes a great pack goat too!
ive heard some good about kinders but i dont know how theyd do size wise for cart/packing...there aessentially a small stocky nubian...
another option might be a MINI cow...look into Dexters!