24 hour fitness offers a free 10-day pass program. You can only go in during limited hours (8am - 9pm, i think), but if those hours work for you, it would be a great, easy, and free way to try out the 24 hour near you for 10 days. Also, if you have anyone else in your family trying to pick a gym membership, the pass is actually for up to 4 people...just go to here:
http://www.24hourfitness.com/db/promo.list
And print it out! They have you fill out a form when you get there and give you a temporary pass. You have 10 consecutive days to try it out, get a feel for how busy it is at your peak times, and check out any classes you're considering.