Honestly, I think self-study is better. Surrounding yourself with native speakers is, in my opinion, only efficient to develop your speaking skills. The rest, self-study is more efficient.
Well, we need to distinguish a few things. Immersion doesn’t mean only going to school in a foreign country.
I did self-study while I was in any different country.
But for sure, immersion by itself doesn’t mean anything and I always take in consideration immigrants. They can spend their entire life in a foreign country and have a poor knowledge of the language.
So, immersion per se doesn’t mean anything.
But if you self-study (with the tools we have now) + I can go to the bar right now and speak the target language, it’s a BIG HUGE difference.
I will improve my speaking (yes) but I also have the possibility to use straight away what I’m learning, reading, studying, etc.
I can also ask people everything and they will answer. About everything. I can ask about football, history, names, slang, etc. All for free, and I can even have lots of different opinions on the same stuff. They will talk and share, I will learn!
I will also improve my listening which will make easier to my brain to focus on other things.
If I work in the target country I will also improve my writing if I have a job that requires me to write emails or stuff.
My brain won’t have any choice!
I will have so much less distractions and I won’t have to use my own native language all the time, like I do here.
Plus I will have a lot of fun in experiencing a different culture, food, habits and so on. You have a lot of different learning moments that you can’t compare it at home. I can’t!
If I could choose today I would do the same things I’m doing now with LingQ + the target country. I will definitely fuse together the best of these learning methods.