Between mobile and the web, I'd recommend the web. In terms of learning programming however, I'd recommend starting in a language ecosystem where the community values teaching programming to new comers. In my opinion, Racket and Processing are good places to start learning to program:

Racket: https://docs.racket-lang.org/

Processing: https://processing.org/

Most web development tools and nearly all mobile development platform assume that the developer is a professional. The tools are complex. The documentation assumes significant familiarity with programming.

Good luck.