Hi Jorge,
I believe that the only reason anyone would choose the IP/A control is if they have existing servo amps that require analog control (+/- 10vdc). In your case, if you are choosing new servos and amps you will want to go with the more modern step/direction. I am not aware of any drawbacks with step/direction as compared to analog control. If you are selecting new servo motors and amps then consider AC or BLDC over brushed DC servos. Why have brushes in your servos that can wear out? I am not sure about cost however....
Good luck!
Mike