Should I start out as a “junior developer”?
Feature building is a junior developer job. It's also a senior developer job. Feature building is part of any developers job.

QA is testing of those features. If you become a QA specialist you won't be developing features at all. You also won't be using TDD. TDD comes before the code under test. Not after.

QA testers come in two types: manual testers and automation testers.  Automation testers are often feature developers as well.

If someones convinced you that newbies must start in QA they've feeding you crap and I wouldn't want to work there. 

Some shops don't even have QA roles because the developers test the crap out of their own stuff and then hand it to a peer to test it again with fresh eyes. Some do all that and then still hand it to a QA group who spend all day doing nothing but gleefully breaking software.

QA is a speciality in and of itself. It's a mindset as much as it's ever a job title.

But QA is not where newbies need to start and it's not a dumping ground for sub par developers. QA is where you put your best or it's not QA.

At the end of the day, a junior developer is just someone who might learn a thing or two from a senior developer. 

As for the career advice find people doing these jobs and ask them what their day is like. That will tell you what you're likely to learn in those roles.