Mandalay Bay and Luxor have good unobstructed views.... be careful though at the Luxor. When I was there a few months ago (and asked for a room with an airport view), that request could not be accommodated and I ended up with a great view of another part of the hotel. It stunk - I saw nothing from the hotel room.
I would also recommend the Tropicana. I had a great view from the far tower, and the north/south runways were pretty close. OK
, the hotel is not as nice or modern as MGM Grand or even the Luxor, but it is comfortable and will even save you a few bucks! The pool is pretty good too. There is also the San Remo hotel that is REALLY close to the runways but I have never been there or known anyone who stayed there.
If part of the reason you are going to LAS
is to planespot, may I recommend walking south on Las Vegas Blvd to the southwestern tip of the airport (about 1 mile from M Bay). Across the street is a Jack-in-the-Box and a gas station - they sell beer! - and my buddy and I spent a few hours sitting on the bus stop bench watching planes, drinking Mexican beer and eating bad chicken strips. It was great! Depending on the direction of the aircraft, it is hard to imagine being much closer to the action!