As Jim said, you can pick and choose. The Mandalay Bay has the best pool with a "tidal wave" beach. I have stayed at all of them and think the MGM is just too large and no longer kid oriented (with the collapse of their amusement park). You don't have to stay at NYNY to take the roller coaster. The best kid spot is Circus Circus [with the Sahara and things for kids to do as well as being near the Stratosphere) but that's a long cab ride to the Trop.