Well, I think I'd say Clapton. Then again, I don't know much about Vaughan. I've watched a TV concert with Clapton, and it was impressive.
What do I really know about Vaughan? For the tone, (playing also?) he doesn't sound as smooth as Clapton.
No, I am afraid I don't know enough about both, especially SRV, to claim very much.
How do they differ in terms of playing? Both are great blues artists from what I know.