Acrylic is easy to get scratches. The tank can be scratched by sharp or coarse things.
Glass is very difficult to scratch. Scratching glass usually requires a relatively hard material and a considerably amount of pressure.
Acrylic tanks are lighter than glass tanks. This means that if you have to move an acrylic tank for some reason, it will be much easier.
Glass is denser and therefore heavier than acrylic. A glass tank will often weigh 4-10 times as much as an acrylic tank of the same volume.
A sharp impact will crack - or in extreme cases, shatter - a glass tank, or at least one of its sides.
Though a VERY sharp impact will crack or shatter a piece of acrylic, the amount of force needed for this damage is far greater than it is with a glass tank.
Acrylic has nearly the same index of refraction as water. This means that when you see a fish in an acrylic tank, the light has only be bent once or twice. Because of this, the only distortion you are likely to see is that the fish is slightly misplaced, but the size and color are true.
Glass has a different index of refraction than water. This means that as light passes through the air, then the glass, then the water to bounce off a fish and get reflected back through the water, then the glass, then the air, the light is bent four times. Each time the light is bent, the image is distorted. Colors are not quite true, position is not quite accurate, size can be distorted slightly. The thicker the glass is, the more pronounced these errors become. This means that in tanks with particularly thick walls, the fish can be significantly distorted.
Many types of acrylic will yellow with age, particularly if they are kept under a full spectrum light or are exposed to direct sunlight.
Glass maintains its clarity over time.
Acrylic tanks tend to be more expensive than glass tanks.More often is due to the shipping. In many cases it will cost less to make the acrylic tank, but the acrylic tank need more care and efforts by the manufacturers and shippers during transportation.
Glass is easier to ship and requires fewer specialized tools to work with, so glass tanks tend to be less expensive than acrylic tanks.