Probably 1 in each alliance, and crafting alts for the rest.
IMHO, there is very little per-alliance replayability right now. There's some different options in quests, but not enough to make a meaningful impact. The play experience will essentially be the same in a given alliance, unless you happen to find a side-quest or two you forgot the first time.
Yes but I actually mean, is it possible to not do the 50+ zones with one character or would I really miss out for that character?
That way the other zones are also 'new' for an alt.