Should social sharing buttons be at the top or bottom of an article?

I can certainly see arguments for both sides of this one:

Buttons at the top: Easy to find, reliably positioned regardless of the article length. Extreme ease of sharing as you don't have to reach the end of the article to share.

Buttons at the bottom: Ensures your users most likely read or scanned to the bottom of the article rather than sharing the article immediately after reading the headline.

However I am wondering which is superior in terms of conversion. Do users share stories more if the sharing buttons are at the top of bottom of an article?