I'm surprised to hear that you've come across bad reviews for Mandalay Bay. I've been there several times (though, admittedly, I haven't had a room there) and I was impressed each time. It's big - so it's on the same level as the rest of the mega-casinos there (e.g., Winn, Venetian, Bellagio, Mirage) - and it's fairly elegant, too. Personally, I wouldn't have any problems reserving a room there. I'm curious, though - what has been expressed in those bad reviews you mentioned?
There are several major and what I could consider decent casinos in the near vicinity of Mandalay Bay, including the Luxor, New York/New York, and, I believe, MGM. Excalibur is close to Mandalay Bay as well, but Excalibur is a bit too "theme" oriented for me.
If cost isn't a factor, then I would consider staying at these casinos: The Palms, Winn (i.e., the most expensive, newest casino there), the Bellagio, the Venetian, and the Hard Rock. No, I don't think any of them are "close" to Mandalay Bay, which is to say they aren't right across the street. But, really, everything is fairly condensed, and nothing is further than a relatively short cab ride away. So, if I had my way, I'd shack up at, say, a Playboy suite at The Palms and just cab it to the Mandalay Bay for the work stuff.