pronouns - different from them vs. different from themselves

"Some people choose friends who are different from themselves, while others choose friends who are similar to themselves."

"Some people choose friends who are different from them, while others choose friends who are similar to them."

Which is correct? Or both?

The sentence "Some people choose friends who are different from themselves, while others choose friends who are similar to themselves." comes from a list of essay topics compiled by ETS (Educational Testing Service).