I've used several versions of FileZilla for uploading and downloading files to my websites during building and maintenance. Though it is a little clunky, especially its interface (being something like an old Windows style), I've found it excellent and effortless and reliable. Even when other FTP programs wouldn't connect for odd reasons, FileZilla just carried on as though nothing was up. I love it. It's easy and clear to navigate local and remote files and folders and shows clear info for upload and download status, size etc.
I haven't found any 'folder sync' function but then again I never use that so haven't looked very hard.