The Sheraton is in a much nicer area of town. It is located in North Scottsdale. There are many options for shopping, dining, and entertainment in this upscale area.
The Legacy Golf Resort, on the other hand, is in South Phoenix. The immediate neighborhood is fine, but it is close to some really bad areas. As a result, it is much more isolated from the places you're likely to want to visit. You don't want to just drive around aimlessly from this location.
As for the resorts themselves, Legacy Golf Resort has much more spacious grounds than the Sheraton, but I would say that the quality of the two resorts is pretty equal.
The best timeshares in the greater Phoenix area are: Four Seasons Aviara, Westin Kierland Villas, and Marriott's Canyon Villas...but all three exchange in II. I think you have chosen the best two choices for RCI.
Steve