I take a taxi-brousse from Sambava to Ambilobe. If travelling by bus to the Northern part of Madagascar, it is usually a good idea to break up your trip into 2 parts. Amilobe is strategically located for this purpose. After resting up there for a day or 2 you can continue to: Diego Suarez or 1 of the cities on the East Coast: Sambava, Vohemar or Antalaha.