As to having a TV channel to speak about Buddhism, we already have it in Taiwan: the Buddhist Tzu-Chi Relief Foundation founded by Master Cheng Yen. This foundation has a TV channel that broadcasts over Taiwan as well as over the world, whoever subscribes it from the website. It starts off with having the Master speaks about some Dhamma passages in the dawn to inspire people to begin their days with Dhamma, with mindfulness and compassion, and throughout the day, the channel features programs concerning humanitarian projects carried out by its members and others, whatever thought to fit into nurturing people with compassion, humanity and wisdom. In this respect, I don't find this as 'evangelical' like Billy Graham or other Christian channels in the United States. I'm not sure about other Buddhist channels in other countries, but I generally find that such activity seems more human-based and pragmatic in human's life and not of evangelism - it serves to nurture certain beneficial values in humans so that we can all create a wonderful and better world to live in. Not so much of like persuading you to accept certain doctrinal truths - no offense to other religions though.
Somebody points out a very good point earlier that the best teacher should be a person who has been well-established in the practice himself, and I find this is what the Buddha preached himself too in Culasihanada Sutta: http://tipitaka.wikia.com/wiki/Culasihanada_Sutta
In addition to this (meaning the above criterion is the main determinant), my personal view is that a person who wishes to speak or propagate the Dhamma should also possess several characteristics so that the Dhamma-propagation effort would be somewhat fruitful or leading toward success - observant in people's responses toward the Dhamma, looking how Dhamma could be practiced in daily life and how Dhamma could be used to solve life problems (this is why a teacher should also be a practitioner) since generally people nowadays would only turn to things that they could find useful to solve their life dilemmas, ability to customize the different needs of people for different aspects of Dhamma, ability to speak the Dhamma efficaciously using certain terminology or examples to convey the ideas (this includes the person speaking from his experience of practice as well as his theoretical learning in order to use the correct terms), etc. These are just my general observations about great Dhamma teachers who have greatly impacted my life, so I hope these characters should be emulated in the Dhamma propagation efforts. Sadhu!