Ask Hacker News: Picking code for mainframe jobs

I'm currently working as a mainframe operator, but my career aspirations lie in programming. I'm being granted an opportunity to learn more JCL, which is the language used to control jobs on z/OS mainframes.

I'm currently studying "z/OS JCL" by Gary DeWard Brown, and one of the first exercises has me programming a really simple job. However, none of the examples use straight JCL. Instead, they utilize (respectively) COBOL, PL/I, FORTRAN, and C/C++. I'm encouraged to use the language I'm most comfortable with, however, I have no practical experience with any of these languages.

This could be a defining moment for my early career. The code I choose to utilize will probably be the one I work with for the extent of my time with JCL. Therefore, I'd like to pick one that will make me a "better programmer" and more desirable to future employers. Please advise.