Everyone has different needs and processes. I tried a lot of them including Zotero and Mendeley and in the end chose Bookends, which has worked out very well for me. I find it better than Endnote for what I need and it is also way inexpensive. The support is very quick and helpful. And it is 64-bit. You might want to check any of these out but I do recommend Bookends for most Mac users.