IMHO before you choose a protocol, you need to choose a media format. If you need to broadcast video streams, flash video is one of the best options, because most users can watch such videos on most operating systems including Windows and Mac OS.

Although all videos can be recorded with screen video capture software and even secure RTMPE video can be recorded, RTMPE protocol is probably the best option for secure videos. For other videos you can use HTTP protocol; it will require less system resources than secure RTMPE protocol.