While the 1mg contains more alprazolam, the extended release will release the alprazolam more slowly. So instead of taking a regular xanax 0.5mg and having it hit all at once in about 30-60minutes, the 1mg will more aplrazolam but over a longer period of time. So you do get more medicine but not in the same way as if you took 2 x0.5mg of regular Xanax. To me, Xanax XR feels more like Klonopin than regular release xanax. It doesn't hit me as hard, but it lasts longer.
It's all personal preference but in an ideal world, I'd prefer having an infinite amount of regular release because it hits harder. Now if I'm limited in the amount of benzos I have and I need an all day sort of fix, then I would chose the XR. Personal preferences..