I'll say two things. First, the chart for the box sub shows a flatter response, which I think is a good thing. The response in your room will be different, though, so real-world differences between the cylinder and box might not be that noticeable.
Second, I have one of their cylinder subs and love it. I have the PC13-Ultra, so it's a bit bigger than the one that you're looking at. I really like the form factor. I went between getting a box or a cylinder for over a year, and I'm happy with my choice. Many others are very happy with their SVS box subs, too. I don't think that you could go wrong either way. It's just whatever seems best to you.