Which is nicer? Are they pretty much on par with eachother?

Bellagio is far and away the best casino hotel in LV. MB is not on the same level, unless you're focusing more on pool activities than anything else.
MB and Venetian are the next best casino hotels in LV after Bellagio.
MB's location is a big negative. But its casino is very nice, great restaurants, great pools.

I would choose Bellagio over Mandalay.

Bellagio is:
* upscale
* higher-end
* graceful
* mature
* low key by the pool
* low key, refined in the casino
* great location

Mandalay is:
* mid range
* a "pretty nice hotel"
* exciting, party atmosphere
* younger
* lots of action by the pool
* far away location
* lots of interesting dining options
* worth visiting to eat there

Why not stay at both? We stayed 2 nites each at both a few years ago and it was great. Had a room overlooking fountains at Bellagio and it was outstanding. As beautiful and elegant as Bellagio is, I liked the atmosphere at Mandalay Bay a bit better, less formal and more relaxing. Im glad we got to experience both tho!

The only place to stay in LV is the Bellagio...period

x, that's the only place for you, perhaps. but give me the beach at mandalay any day!

I generally agree with the posts that Bellagio is probably the top hotel in the city, followed by Mandalay Bay and Venetian. So if Bellagio would be rated a "5", Mandalay Would probably be a "4" or "4 1/2". All things being equal, I would choose Bellagio, not so much for the hotel itself but for the mid-strip location. I've never actually stayed at Bellagio, however, and haven't seen its pool area. Mandalay Bay has a great pool/beach, the only down side being that it can get very crowded on weekends.

Bellagio