Of these, HTTP is the preferred choice since it works with corporate firewalls and does not open up security problems.
More information follows.
If remote users can connect to the FTP server but cannot list or transfer files, they need to put their FTP client into non-passive mode. Remote users may upload files into the incoming directory. Any remote user also has permission to delete any files in the incoming directory, even if they did not place the files there originally. To copy uploaded files to your home directory, simply FTP to the server and use the get command. Then use the del command to delete the file you transferred from the incoming directory.