If you're looking for advice on which is generally the better quality boot, they are both top-notch manufacturers. Others of similar quality are Lowa, Zamerberlain, Civetta. I think Limmers were mentioned above as well. Great boots, but custom. You have them made to fit your feet.
The Glacier is on the verge of a heavy-duty backpacking boot and is meant for heavy packs an rougher terrain. The idea is that if you are carrying heavy wieght, say 50-70lbs range, a lighter boot is not going to support your foot, arch, ankle, etc. The combined weight of you and your pack will simply overwelm the structure of boot. If you were to walk across a scree slope heavily laden with light boots, the pointy rocks would jam up into your foot. The heavy weight pushes you down and the lightweight soles just aren't enough to protect your tootsies. The more weight you carry, the more flexible the boot feels. The Scarpa is not quite as heavy duty, but it's by no means a lightweith boot.
If you are going lighter weight, these boots may not be as comfortable, or may take longer to "break in" to the point that they feel comfortable. When I backpack with less than 40 lbs in my pack, I use a fairly lightweight boot called the Lowa Jannu Mid. Lowa doesn't make them anymore, but they have something similar. It is comparable to the Vasque Sundowner. Between the two boots you have, it's closer to the Scarpa.
Neither boot is really a true "mountaineer's" boot. I don't believe the Scarpa has a shank, or if it does, its probably nylon. The Glacier has a half-shank. Neither is designed to accept crampons. The Makalu from La Sportiva, for example, has a sole designed for crampons and a full steel shank; it's one mondo-stiff mountain boot.
Once you break the Scarpa in, it will probably serve you well as a decent hiking boot and a good all-around backpacking boot. The Glacier will be for heavier-duty applications.
If you hike more than you backpack, look at something a little lighter. Most people just use trail runners to hike in these days. I have to admit, I do most of my hiking in a pair of Scapra Zen "approach" shoes, which is a hybrid between a rock climbing shoe and a trial runner.
Good luck and have fun in your research; as I said, they're both great boots!
Eric G.