i think you have to evaluate what is important to you in a gym and evaluate each one:
are lots of classes important or could you not care less?
are free weights and power racks important to you?
are you a cardio-bunny and need lots of treadmills and ellipicals available at peak hours?
what time do you like to go and how crowded is it at that time - and are you ok with that?
do you like a social crowd or are you a heads-down-let-me-get-my-workout-in type?
do you need childcare facilities, a pool, other amenities or just-the-gym please ?

etc.