Husband has owned both.
He says the Arbor is a stiffer, wide board. It is regular camber and great for carving and cruising the mountain. Decent powder board.
The Legacy is a bit softer, and a mid-wide, camber-rocker combination. Great board for all-mountain. Does well in the park, on pow, and on groomers.
Both companies make great boards. Hubby prefers the Legacy, as he finds it more playful.