I would recommend visiting both, and getting shown around. They may offer you a free day/week pass to try to get you to sign up with them. I would try a workout at both places and decide. See who has the better pricing, and what you get for your money (trainers, etc). See how long they require you sign a contract for, or if they allow month to month. (I believe Bally's now offers month to month? I could be mistaken.)
If the Gold's is closer/more convenient, then that's probably the better bet. Those times you get off work and are tired, unmotivated, etc, it would be easier to talk yourself out of going to a gym that's further away or less convenient. The gym I train at now is about 5 minutes away, so if I'm running late, weather is bad, tired from work, etc, it's a lot easier to motivate myself to go. If it was further away, it might be easier to 'go tomorrow'.
ETA: I hate the local Gold's, but I think that's because of the local management, and not the entire chain. Long story.