Bellagio - my favorite...everything there is beautiful...the lobby, the rooms, the gardens, the artwork. Even the casino smells good. Great restaurants and shopping.
Caesar?s Palace - Nice if you're looking for old-school Vegas ambiance
Excalibur - don't like it, too many kids
Four Seasons - never been
Hard Rock - great if you're looking to party but I think the rooms are very over-priced for what they give you. All night room service is a plus
Luxor - really nice
Mandalay - eh, nice but the few times I've walked through the casino, it smelled like sewage. House of Blues gift shop is way overpriced.
MGM Grand - my second favorite, but my only complaint is, the elevators seem really far most of the rooms and I've always had a looooong walk back to my room. Great restaurants, nice casino.
Mirage - nice rooms
New York, New York - really fun place to gamble, scarier than hell roller coaster but again, too many kids
Treasure Island - yuck
Venetian - Beautiful casino but I've never stayed there