The best location is Flamingo and 215. Great place to work out. Lots of people there at all hours, so it is good to people watch while working out. If you go during the busy hours, you may wait for equipment. I usually go during the off hours, and the one at Rainbow and the 95, which is a lot bigger and less packed. I've only used the cardio and weight sections, so I can't comment on the pool and spa area.
The other thing is that a lot of healthy fast food places, nutrition stores, and tanning places are located very close, making everything convenient.