Def. go with MGM. Its location is better than Mandalay and their poker room is also much better than Mandalay Bay.
And Venetian > MGM because its location is much better. From the Venetian you can walk to Caesars, Wynn, Bellagio, Mirage, TI, Harrahs, Ballys, Shuttles to Rio. While the only okay places to play poker near MGM are at the MGM and Mandalay. Unless you want to go crazy at the Luxor's $50max buyin 1/2nl game. Big money, big prizes...