Hitchens, definitely; he’s my spirit animal.

Hitchens was the most gifted orator, with preditory skills in a debate.
Sam Harris is the most pacific articulate one who delivers his ideas with a surgeon like precision.
Dawkins is flamboyant. And Dennet is a great thinker.

For me it's Dawkins, Hitchens, Harris, and Dennet.

Dawkins first because I also studied Evolutionary Biology and I was just naturally drawn to his works on evolution and atheism.

Hitchens is a very close second just because of how eloquent he was and the way he could masterfully match anyone on the debate stage.

Harris third because I always enjoy reading his philosophical perspective.

Dennet fourth because (as ZenBear said) he was just never that active or involved. At least, he didn't seem like it to me.

All of the above! #1 Hitch #2 Harris #3 Dawkins #4 Dennet. Hitch is my fav because of his unparalleled oratory sophistication, Dennet last only because he was never as active as the others.