I loved zotfile for its feature which enable user to highlight/comment articles then import the text in notes related to article.
The one downside of this approach is that multiple people can't modify the same PDF at the same time. The upside is that you can use whatever PDF tools you want and annotations remain accessible in the file even if you stop using Zotero, which goes with our philosophy of leaving people in control of their own data. (Mendeley stores annotations and highlights in its own encrypted database, and you can't even export PDFs with annotations in batch. If you want to get a PDF with your annotations out of Mendeley, you have to do it one file at a time.)
Disclosure: Zotero developer