Mandalay Bay is a great hotel for spotting especially since its a much taller building than Luxor or MGM, which makes for better viewing of all the runways. LIke shown in the pictures above the planes takes off towards the west and flies right next to the hotel.
I have also stayed at The Hard Rock Hotel, the hotel is a little far from the airport but depending on how they are landing at LAS
, the planes passes right next to the hotel on approach. Then from the balcony you can see part of the airport and its runway. Claearly, was able to make out the planes such as JAL, UA
even from the distance.