I currently Papers for PDF management, and Endnote for reference management while writing. They each have useful and complementary features, but neither is a complete solution and they don't work well together. Any recommendations out there?
I use Mendeley for both. I find it easy to use (and easy to learn to use). It's more simple than EndNote. I store all my PDFs on Mendeley as well. The only downside to Mendeley is that its not as popular as EndNote so sometimes shortcuts that are available for EndNote aren't available for Mendeley (although a lot of them are - eg Mendeley is compatible with NVivo etc). Also its good with EndNote that everyone knows how to use it so if you need help there are heaps of people who can help you - there are less with Mendeley although I've found it very easy to find answers on the net whenever I've had queries.
I use Endnote for both as allows you to include the pdf along with the citation in the library. These can be added relatively easily manually or automatically using the 'full text' option. Requires relevant institutional subscriptions to the publishers and would need to be enabled by your institution's library to authenticate Endnote access.
The biggest minus of Mendeley, for me, is that it uses csl — citation style language, which is difficult to modify unless you have some programming experience. As a result, I just cannot adjust the citation style to my needs. Same applies to the majority of reference managers (including Zotero, Papers). EndNote provides a possibility to modify the citation style as you wish, and it doesn't require any particular skills. Although the pdf organization in EndNote is poor, especially if you use X7 version on MacOS Sierra, where it has tons of bugs. The only reference software that combines the commodity of Mendeley (or Papers) with functionality of EndNote (at least the only one I know of) is Bookends. Try to consider using it!
I find Zotero works great for me for both storage of pdfs when available, creating reference lists in just about any citation style, and in-text citation. It works best within the Firefox browser, but it does work (with an add-on) with most major web browsers.
If you want something to do all of the above I would chose the: Zotero + Zotfile + Better BibTeX combo. I explain why in this article (https://medium.com/@granieriniccolo/fantastic-reference-managers-and-where-to-find-them-a412621eb4ba) but I found it to be the best free alternative.