That depends upon what you want to build. If you want to learn a well-established framework with a great community and lots of free online content to learn from I would suggest looking at Ruby/Rails(although lot of folks would argue that Django fits that bill too).
If you want to learn web dev but also are looking at other domains like scraping/ML etc you should pick python/django.
Anyway the more important point here is that you can't go wrong with either, pick one and get going!