There are hundreds of scope options on the market, from red dots to magnified, or even laser sights for AR-15, leaving you with a huge decision to make.
A fixed scope can work well for sports purposes where you have to shoot at close ranges. However, the most versatile scope for an AR-15 is the variable scope which gives you good speed up close and great precision when shooting at long ranges.
For long range shooting, you need variable long range scope to gain more shooting capabilities. You can easily nail down targets from distances of 600 yards using variable long range scope as compared to fixed scopes.