The answer above is already pretty good, I'd say!
In my experience, the the immersion method really accelerates conversational skills because you're living the language every day. When I was immersed in a German-speaking environment, I noticed my fluency improved much faster than it ever did in a classroom. That said, traditional classroom learning gave me a solid grasp of grammar and writing, which I struggled to pick up on the go.
Combining both methods was great for me, in the end. Immersion helped me with reading and listening, and 1:1 classes were great to have some questions answered (and to practice speaking, obviously).