Would pick Matt Dillahunty or Pat Condell. Douglass Murray, Stephen Fry, and Seth Andrews deserve mention as well. They are all highly authoritative, persuasive speakers. Matt and Seth lack the suave humor of the other three, and Seth lacks lacks the biting bluntness of the other four.

I'd have to agree with the Krauss pick.

Though I love Matt and Aron my personal favorite is Seth Andrews.

Neil DeGrass Tyson or Stephen Fry

Sam Harris

Yes, Lawrence Krauss. And I would like the horsemen thing replaced by horse people. There are a lot of very active women in the atheist movement, look at Richard Dawkins site for example, but the leading activists Dawkins etc are thought of a group of men. It gets criticised for that. I would like to see that change. I also have to say that, despite the obvious sadness of his death, that Hitchens was my least favourite horseman. Liked his views on religion, but not his politics.

Krauss is my pick, too. His name was in my head before I even got to the end of your post.
He's also got a great sense of humor, which is vital.

Matt Dillahunty or Aron Ra. Both are excellent at what they do and are sort of my yin and yang duo. Though I think I'd lean in Aron Ra direction if we are to replace Hitchens with someone similar in their 'take no bullshit' attitude.

Umm, me?!

Matt Dillahunty without question. Krauss has this going against him: