IMO opinion a fountain view room at the Bellagio (with dinner at Picasso) will take some beating. Other hotels worth considering though are

The Wynn Hotel
TheHOTEL at Mandalay Bay
The Four Seasons Hotel

If you are looking for a super hotel which is less like a mega Casino resort I think the Four Seasons will be best. It is to be found on the top few floors of the Mandalay Bay hotel - but has its own entrance, lobby, restaurants, pool, spa etc - But no casino -this is a short walk along a corridor from the hotel lobby. The Four Seasons doesn't get very much through traffic from the Mandalay Bay Casino so it is relatively peaceful compaired with the other hotels which are all Mega resorts with 1000s and 1000s of guests.