If you're in the San Diego area you should have a LOT of places to choose from!
Most gym chains and some independents offer free visit coupons (check their websites). I know that currently 24 Hour Fitness is offering deals, etc tied in with their sponsorship of the show "The Biggest Loser". I would encourage you to get ahold of some of those coupons and go to the gym at the times that YOU would go to see how crowded (or not) it is at that time.
I just checked smartpages.com for the SD area and see that Bally's has a 2 week free guest pass available for download.
If you're signing up as a couple, usually gyms offer special couple/family deals.