I agree with the majority of the other posters; internal is typically best. In my experience, usually how this plays out is: 1. Establish yourself has a high performing SSE. You need to build this reputation both on your direct team and department, but ideally across the org broadly. 2. Make it known you wish to become a manager at some point in the future. Have conversations with your direct manager, but also consid…
Well, on a random 1:1, manager said "Oh, by the way, the team is growing and is too big for just me. We couldn't find a good internal candidate so we hired a new manager for you guys externally. Hope it works out!" Finally, at this point, way too late I said "Gee, I was kind of hoping to make that move myself!" Manager looked at me mystified that I'd be interested in career growth. Total miscommunication. I was really bummed, demotivated, disgusted, lots of negative emotions. I didn't even last another year there.
Don't do what I did :)