In the following video, Fool.com contributor John Reeves sits down with Fool analyst Buck Hartzell to hear why Berkshire Hathaway (NYSE:BRK-A) (NYSE:BRK-B) and Markel (NYSE:MKL) are Buck's two largest holdings right now. He tells us what he loves about these companies, what has driven their success in the past year, and whether investors should think about buying today.