I've been digging into various Mozart biographies in recent months, with varying success, and by far the most enlightening and readable is Mozart in Vienna, 1781-1791, by Volkmar Braunbehrens (pub. Deutsch 1990).
It sets Mozart very firmly into the Vienna of his day, and does so entertainingly and vividly. It has no truck with uncritical acceptance of Mozart myth, and makes a serious attempt to distinguish fact from fiction. It's the sort of book that makes you wish, when you're halfway through, it were twice as long as it is. And even better, it makes you want to go and listen to more Mozart.