If you're just starting out and your experience thus far has been python / django then I'd say go for the .net job.

While .net itself may not be "cool" you'll benefit a lot from diving into an entirely different language, framework and ecosystem. Plus, it sounds like you may get some good mentorship, which is invaluable when you're starting out.

Bottom line: don't sweat the .net - dive into a different stack, spend a few years learning its way of doing things and then see what you want to jump into next.