I'm guessing you're in Toronto. Both are about the same in terms of cost. Prob about $30/every 2 weeks. Depends what you want. The Goodlife gyms are a little older, but have an older clientele, and are a little less judgemental. Extreme is rennovated like every 6 months and has a younger clientele - although they're usually a little more hardcore and might be more intimidating.
Go to the ones nearest you and ask for a tour. See what machines they have, what deals are on, how clean the locker room is, if the weightroom seems messy, how many classes they have (if that's your thing) and if the staff seem friendly. You'll know which one to go with based on your gut feeling.