Who do you think has been most impressive this season?

As much as I want to say Mark Martin, I can't help but think that Tony Stewart has been the most impressive. Yes, Mark has 2 wins already, but did any one really doubt that he would win? Especially with Hendrick equipment. Tony is in the first year as an owner-driver, and has been fairly consistent, and it's only a matter of when he'll win, not if he'll win. The more races he finishes in the top 5, the more I think he'll win some races this year.