The downside of an acrylic aquarium is that cleaning coralline algae is very annoying and you are going to scratch it, and it just doesn't have the crystal clear look of low iron glass. The benefits are the incredible durability and the much lower weight. I have a very large tank so for me the weight savings and durability of acrylic was the most important concern, but cleaning the sides is constantly annoying, and if you get a little careless it is very easy to scratch. Granted, it is also fairly easy to remove the scratches, but I'm too lazy for that so I just live with the scratches.
My personal rules of thumb would be if I was setting up a tank <120 gallons I would 100% get a glass tank. 120-250 I'd think about it and >250 I'd go acrylic.