We have stayed at MGM signature several times and really enjoy the extra space these rooms have. This was our first time however using Las Vegas Suites to book the room.
Price- the rates were significantly cheaper but it does not include housekeeping. You have to pay extra to have housekeeping during your stay.
Quality- the view our room had was amazing and we were in tower 1 which was nice because it was close. The issue I have with the quality is the room was shabby...the walls had smudges, the furniture was worn. Overall the room needs to be retouched. I know from other stays at MGM that rooms we booked through MGM directly are much better kept.
The only other issue is availability of the Las Vegas suite staff. They keep banker like hours so you better make sure you get questions answered before the weekend and before 4:30pm on weekdays...