My glass selection is as follows:
(I've listed them in order of expense from lowest to highest)
Regular Clear glass - Self explanatory.
Conservation clear - Clear glass with an ultraviolet filter to help prevent fading. I recommend this for a piece that will receive direct sunlight or will be hanging in a room that is lit with flourescent light.
Reflection control (non-glare) - For pieces where glare is a problem. This is better than the "old fashioned" non-glare but tends to get fuzzier as it gets farther away from the piece. I don't recommend it for pieces with more than one mat.
Conservation reflection control - This is a non-glare glass with an ultraviolet filter to help prevent fading. I don't recommend this glass for pieces with more than one mat.
ArtGlass - This is the clearest glass you can get. It seems to disappear in some light sources. It tends to be very expensive. It has an ultraviolet filter to help prevent fading. It's ideal for heirloom pieces.
I no longer recommend Anti-reflective glass. It's a beautiful product, but I feel that if you're going to spend that much money on glass you might as well use ArtGlass and get the added benefit of ultraviolet protection.