Noise
A curved blade cut into the air less than a straight blade. This creates less noise, so curved-blade fans are usually much quieter than a fan with straight blades.
Performance
Although curved blades are quieter, the reduction in noise comes at a price. Curved blades move less air than straight blades, creating a less powerful breeze than a traditional straight blade.
Choice
If you are easily bothered by fan noise, then a curved-blade fan should appeal to you because it is quieter. But if you want maximum performance out of a fan, a straight-blade fan is probably the way to go, even if it is a little louder. Other factors that can contribute to a fan's noise are the materials of which it is made, and the insulation around the motor.