On my iPad, I have GoodReader, as well as ReaddleDocs, and both allow me to connect to a large assortment of Cloud Storage providers. On my Windows machine, there are the Cloudberry Lab assortment of products. On my Mac, there are less options.
I have a license for Syncovery, and have been using it since it was called "Super Flexible File Syncronizer". It works great for large pushs and pulls, but doesn't have a great GUI. It also doesn't support as large of an assortment a I would like.
I found Interarchy 10 and DragonDisk. However, the best front-runner right now is CyberDuck, though the GUI is not super shinny.
Am I missing any options? Paid or free is fine, as I don't mind supporting any developers for work they do. If it can have the Mac skin to it, it would be awesome!