To the Roddick fans, for a while, he had the biggest forehand and serve combination in tennis history. Bigger than Pete... bigger than Becker... bigger than Lendl. Perhaps not the best, but the biggest. In a practice session in Armstrong Stadium against Robby Ginepri back in 2000 or so, he hit one of the biggest forehands I've ever seen. Combine that with a serve that routinely hits the mid 130's, and we're talking serious power.
But besides his serve, Roddick is not as powerful as Del Potro. Roddick's backhand is a loopy, keep-me-in-the-point kind of shot. Not saying that's not a good thing, I'm not talking about the best tennis, just the most overall power. Roddick is more opportunistic, he can't generate the effortless power off the ground that Del Potro can't, his stroke production just isn't the same. When Roddick goes for power, you can SEE the effort, and he must wait for moments. With Del Potro, he's hitting hard effortlessly, and just as effortlessly, he suddenly hits something nuclear. And he doesn't necessarily have to wait for the right moment.
I've been high on Del Potro since I saw him at the 2003 Us Open qualies. On a different board, predicted he would be top 10. Not just jumping on the band wagon, even then, he could put some insane heat on the ball. And the crazy thing is he still has big room for improvement. Right now, he's basically hitting people off the court with incredibly sound groundstrokes. He's not swinging for the fences, his regular body shot is pretty tough to handle. But his point construction and transition game can use some work. And his serve was good in 2003, but it's way better now, and I think it's only going to get better. Against Fed, he was mostly hitting slices in the 5th set, and it was enough to give Fed fits. Scary.