I personally learn best in a course with a teacher and with other students. I have done one-on-one lessons before, and this works for some people, but I need the opportunity to practice speaking with others who are not as good at the target language as well. I prefer to have this be frequent (like daily or 3x a week). I can and do learn quickly with one.
I do have a friend who learns very well from books, online resources, and private tutoring, and he learned Chinese in about a year to a pretty solid level, after which point he went to China for study abroad. But that’s not me, I prefer a class.