The Canon 75-300mm and 55-250mm lenses are two relatively inexpensive telephoto lenses in the Canon lineup, making them popular with hobbyist photographers. While both lenses are capable of delivering quality images, there are several differences between the two that you should consider before purchasing each one, regardless of which focal length you actually need.
The 75-300mm lens is available in two different models: one has an ultrasonic focusing motor, one does not. The one with the focusing motor, labeled a USM lens, will focus on objects that are far away much quicker than one without. The 55-250mm lens does not have an ultrasonic motor.