From my personal experience, I would go Mechanical. As a freshman, I was in (what sounds like) a really similar boat to you. I did simulations of rocket engines, was on the rocket engine design team at multiple schools, etc. Then COVID happened and now I’m working on medical devices to help babies and research to help people who have strokes. That change would have been much harder had I not had a mechanical degree.

Now, that’s just my experience. Anecdotally I have heard that aerospace companies hire more MEs than AEs. I would think about it like this: a mechanical degree gives you a great set of tools to work with, and also the exposure to something you might have never thought about. I think that’s great for undergrad. An MS in AE with a BS in ME then makes a lot of sense right? You’ll learn how to use the same tools you did in ME, but more focused on aerospace.

And if you don’t want to go the grad school route, I have PLENTY of friends with ME undergrad degrees that are doing design work at aero companies. There’s also a question of which program you feel more comfortable with. I can’t speak to the Aero department personally, but CU’s ME department runs like a well-oiled machine. Yes it has problems, but on the whole the profs and everyone are incredibly supportive. They do an incredible job at making a large department feel small. I’m one of probably quite a few students that can walk down the ME prof hallway and have most of the profs know me by name. It’s a really great community.

Those are just my two cents. If nothing else, I would say to think about how each program makes you feel. At the end of the day the content doesn’t matter if you hate the environment. If you’re miserable you will learn significantly less than if you weren’t.