I couldn’t think of any reason that would once and for all decide if motors should be mounted on the towers or mid-section of the DR4B. There are cases where either of the methods could have more advantages.
If the design calls for two DR4B motors and dual towers, then it could be easier to mount motors on each tower. For a single tower design, you could put one motor on the tower and another on the mid-section.
Having dual motors mounted on the mid-section could also make it easier to mechanically connect the pinion gears on the left and right sides of the lift to ensure it doesn’t lean to one side.
In this specific case, where DR4B will have just one (V5) motor, it makes sense to put it on the mid-section. It will need one less 60T gear and will be 1" more compact in the horizontal dimension.
If the lift is properly rubber-banded the effect of the motor’s weight is not that significant compared to the weight of the intake and the game object(s) on the end of the lift.
Finally, for the more advanced designs, where you want to use dual motors in the differential configuration (like @ZachDaChampion of team 77788J did here ) then placement of the motors will depend on whether you want to send secondary function power down toward the chassis or upward toward the top of the lift.