GoNC - 10:21 pm on Jan 17, 2014 (gmt 0)
According to this, it was:
MySpace had a much higher percentage of 18-20 year olds (debatably adults), and a slightly higher percentage of 45-54 year olds. 25-29 was virtually the same between MySpace and FB.
An excellent point was made in the comments of that article, though. I read a report awhile back that said more than 33% of the accounts on FB are fake (the report referred to duplicate accounts for games, but I think the % is higher due to scammers), so you can't really trust the demographic data on FB.