Where do most commercial airline pilots like to fly in the atmosphere? Why?

The main reason airplanes fly in the stratosphere is because this is where the least amount of turbulence is found. In addition, because the stratosphere is very dry, there are fewer clouds in this layer, making for a much smoother ride overall.

Explanation:

Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below. The stratosphere is very dry; air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere.