To solve this question, the user needs to know the basic concepts of IBM Mainframe and the purpose of each utility mentioned in the options.

IEFBR14 is a dummy utility that does not perform any function but returns a completion code. Thus, option A is not used for comparing sequential files/PDS.

IEBCOPY is used for copying Partitioned Data Set (PDS), Partitioned Data Set Extended (PDSE), or Sequential Data Set (SDS) members. Thus, option B is not used for comparing sequential files/PDS.

IEBGENER is used to copy or generate a new dataset. It can be used to generate a sequential dataset from a partitioned dataset member, or copy a dataset to another dataset. Thus, option C is not used for comparing sequential files/PDS.

IEBCOMPR is used to compare two sequential files or PDS. It compares each record in one file with its corresponding record in the other file and produces a report of the differences. Thus, option D is the correct option used for comparing sequential files/PDS.

Therefore, the answer is: D. IEBCOMPR.