There are a lot of threads on this, it always comes down to: weight (acrylic pro), scratching (acrylic con), cost (typically acrylic con) and clarity (acrylic pro, unless starfire or some low iron glass). I personally prefer acrylic because of lighter weight for large aquariums.
The benfits of glass is they are harder to scratch. But acrylic has come a long way in regard to scratches. Now acrylic is much lighter. But I prefer glass.