Slowed muscular movement of the esophagus is typically due to either muscle or neural dysfunction, so it's a motility disorder. Both prilosec and prevacid are used to prevent acid reflux issues decreasing the amount of acid that is produced in the stomach. Neither of these drugs will affect the motility of the esophagus in any manner.
But if the meds are being used to decrease the acid levels so that less may be present to reflux into the esophagus, then it's going to be a matter of trial-and-error. Medications affect each person differently. A medication that works optimally for one person may work sub-optimally for another.