There seem to be a number of parameters to bear in mind. You want decent humane people, who can work together and give a good impression of our species. You want a good selection of types of people, in such matters as ethnicity, religion, gender, etc. And finally, and this is the one I find most difficult, you need your council to have the endorsement of the global population, so you need to include representatives of all the major opinion blocks, or the unrepresented ones will get antsy.
Tricky isn't it?
At the moment I'm thinking: The Dalai Lama, Nelson Mandela, Aung San Suu Kyi, Stephen Hawking, Ursula Le Guin, and Nawal el Saadawi.
On the plus side, this gives me a scientist, and artist, a religious leader, a health expert, a political leader and a rebel. It covers at least four ethnic groups and four continents, and has a good gender balance.
On the negative side - no no chinese or indian representatives, no-one from South America or Australasia. I'd include the Pope, except that he seems too old and feeble to handle it.
What such a council really needs is a starving mother of multiple children from a war zone, and a street-child from South America. But how would you find and nominate one?