Ever since the big UX app overhaul there is not much to like regarding functionality. They removed the pdf renaming and some other major automated file mgmt features from mendeley.

Other than that the commenting and note reader UI was pretty good. And overall UI/UX felt more modern than Zotero, also free (as in beer) cloud backup.

Today I had to do some literature review, and I reinstalled Zotero 7beta because I am not happy with the removed functionality from Mendeley.