The primary reason I went with acrylic was for peace of mind. I plan on having this tank a long time. I felt that acrylic was safer with a tank of this size. Having a personality where I fret over stuff easily, I didn't want to worry about a seam giving way and 427gal of water pouring into my house.
Secondary to safety, was the issue of clarity. Since the tank is in a sunroom, glass would reflect and bounce the sunlight everywhere making viewing harder. Acrylic would not reflect the light anywhere near as much, and is much clearer than glass.
Of course there is the big downside of scratching with acrylic. I have become very adept at buffing out scratches since this is not my first acrylic tank. Even so I miss the ease of cleaning a glass tank. I can say with confidence though that I made the right choice.
I think the decision of glass vs. acrylic depends a large part on the circumstances. If my tank were in a basement, then glass could be a better option. Likewise if I was the type not to clean the tank for weeks at a time, glass would be better. So you have to consider all the personal factors before you decide.
