The main advantage of low iron glass is that it doesn't have the green tint that regular glass has. So the colors of your fish will show better (in theory at least.)
However, low iron glass is considered a "softer" glass so it is more prone to scratches. Also, it is more expensive.
Ideally, before you purchase a tank you should try to compare the look of a tank made with low iron glass and a tank with regular glass if possible.
Best of luck to you.