I'm fairly sure there is less refraction of light in acrylic than glass aquariums, so you should have less distortion of the fish you are looking at. My understanding is glass is stronger than a similar size aquarium. There is the issue of acrylic aquariums possibly turing yellow over time, I think it happens if exposed to direct sunlight, also as others mentioned it scratches easier. Personally I have both. I have a 300gal acrylic, that I would like to replace with a 600gal or 750gal, it will have to be acrylic, no way I would buy a tank that large made of use glass. But if I were rich I would go with low iron glass and make a tank the size of a large pond. Personally I would go with acrylic for tanks larger than 240gal, if I were rich it would be all low iron glass since I wouldn't have to worry about moving it and would have it made thicker than needed.