I dunno, I think it's best to have both a good closed guard and open guard, and then play closed guard first, with open guard to fall back on. I mean, with closed guard, you can still attack, and they can't do anything until they open your guard first, so is that not an ideal situation? You can always open your guard, but it's not always possible to close your guard once it's opened.
I mean, even if you have a great open guard, it's like this: if you have a slingshot and a bat, and some guy is coming at you swinging for the fences with his fists, sure you'd have a big advantage in close with the bat. But isn't it just safer to take some shots with the slingshot before he gets to you, then switch to the bat, rather than charge straight at him with the bat?
I mean, I'm not advocating just lying there and stalling, that would be like turning around and running away in the previous example. I'm just saying, why not attack from the closed guard, from which he can't really do anything back, and then open it if you can't seem to make any headway from closed guard?
Note that my club is primarily no-gi, so that may have some effect on my views.