Digitals give a better "return to zero" than analog. A cheap servo may have 128 positions that it stutters through as the arm swings, a good one 512, and high end almost unlimited positions (1024 & up) within the arc of travel.

In addition to the strength in torque (inch-ounces) the more you pay generally the better the response time, repeatability of travel.

But it makes no sense at all to buy digital servos and attach them to the control surfaces with sloppy or "bendy" control rods and actuators, or with slop in the attachments to the servo arms. This is why you see the ball-joint connectors and aluminum replacement servo arms. For most of us a plain 'ol servo is sufficient for sport flying.