Filezilla. However, I just found out today that Notepad++ had a built in FTP feature so you can manage your entire site pretty easily from it. (for those of you who don't know what Notepad++ is, it's basically like Notepad, but more designed for coding with syntax highlighting and numbering). Unlike Filezilla (if I'm not mistaken), you can edit your files through it. As far as uploading large amounts and/or big files, Filezilla would probably be the better choice.