24 hour fitness is just as they say, open 24 hours. That means no matter what time you want to work out, you can--and this is one less excuse to keep you from fulfilling your New Year's Get Fit Resolution. (I'm not sure if that is a good thing, or not) The gyms tend to be pretty well equipped--from machines to weights, and other things in between.
The major drawback to working out at 24 hour is the cost. There's a large processing fee that is dumped on top of the membership cost. However, they generally tend to run membership specials a few times during the year in which they either waive the fee, or you can have another person join with you for free. Also a huge cost saving method that takes a lot of money up front is to pay for the year's membership in full when you sign up.