I used to use Zotero and Mendeley, but recently switched to Paperpile and haven't looked back. It's a Chrome plugin, and saves all your papers to Google Drive.

I used to use Zotero and Mendeley, but recently switched to Paperpile and haven't looked back. It's a Chrome plugin, and saves all your papers to Google Drive. It has a really nice cite-while-you-write extension for Google Docs that really makes it worth it.