I will add to what others have said. While all above have pointed out pluses of the digital servos there is a minus that needs to be taken into consideration. Digital servos use more power than their analog counterparts. When an analog servo centers the servo moves to the center and WAITS for it's next input. A digital servo moves to center and then it continually updates itself to stay in the center (this is why they buzz). This constant updating uses up power that an analog servo doesn't. This is not a huge deal with the large battery capacities that are available today, but it is something that needs to be considered. If you are moving up from analog servos to digital you will need to increase your battery capacity too.

Ken