It is really hard to answer this question without being provided any information whatsoever. Even though both can be used as full stack, nextjs is more front-end oriented, while django is the opposite. It really depends what you want to build. I personally use both, Django because it is battle tested and a joy to work with, Nextjs when I need a complex ui.
It is somewhat like asking, "python or javascript", without saying if you're talking about doing data science or a frontend-heavy website.