Which sentence sounds the best?

[A Rose for the Dead]

1. Teenage girls' use of social networking sites decreases their self-esteem.

2. The use of social networking sites by teenage girls decreases their self-esteem.

3. The use of social networking sites causes decreased self-esteem in teenage girls.

4. The use of social networking sites decreases teenage girls' self-esteem.

[Phil]

I would consider 2 to be the easiest to read and understand. Apostrophes can be difficult to absorb when reading, and the two objects, girls and social media, are closer together than in 4, which also helps readers to understand it.