I have the one with the 256 MB VRAM card. However, I hear that the benefits aren't noticable at this point (with the current video game titles available). I will tell you that the reason I sprung for the upgrade was longevity. The more you buy now, the longer your computer should last into the next tech curve (theorhetically that is). So, bottom line... if you can wait it out, you might as well do it. If you can't, then you won't really notice the difference for a while.
There are other threads on this subject in this forums, but I think I covered the gist of them.