Glass is a traditional material for constructing aquariums. It is very difficult to scratch. Glass maintains its clarity over time. The glass in a new tank will match that in an old tank. However, glass is relatively rigid and brittle. Because of this, it is difficult to make fish tanks from glass that are not rectangular in shape. Also, when glass is curved, it has a tendency to bend light, making things on the other side of the curved glass appear larger or smaller than they really are.
So, if you want a traditional rectangular medium-sized aquarium, if you don't want to mess with the scratches, and you are not worried about sharp objects shattering the tank, then glass aquarium will be the right choice for you, plus it will save you some cash. However, if you are setting up a very large tank - 500 gallons or more - or you are interested in a tank that is not rectangular in shape, you will probably want to consider acrylic.