I've done both ways and I think the answer is actually a little of column A and a little of column B. I think having a project or an idea that requires this new language is a great way to maintain motivation and consistency in learning, and I think courses have their place as well. I think a good idea is to learn a little bit, build something, learn a little bit, build something. You have to constantly be striving for something that is just out of your reach. I think the project method keeps you constantly striving for just a little bit more.