I tried two main methods (+ some methods like "learn German in x days" and that really give the basics of the language): Assimil and Harraps, Spanish and German and I give my clear preference for Harrap's because it is much more progressive: it seems to advance, turn pages and, of course, to learn. Assimil guess - justement- we assimilate a lot of vocabulary and grammar in a short time, it is above phrases to remember without too much explanation, or learning a new language takes time and that the we understand the mind. As for me, learning by heart does not interest me at all. And Harrap's method gives the time. And I find ultimately more useful in the long term. Furthermore the methodology is well made, with various exercises, crossword puzzles, you want to browse the book, to see / hear the rest. The book is super friendly, which is very important in learning a language because it is a long process, very long! It's perfect for beginners or semi-beginners. The super intensive methods, I gave, including specific course, and I do not believe at all.
NB .: a Sylvain gave one star to the Harrap's method, boasting Assimil. Know first that he copied my own original comment, which I have since completed, replacing Harrap's by Assimil and vice versa - so it defends Assimil - and that is part of the entourage of Assimil, unlike I who have tried the 2 methods and know what I mean. He says qu'Harrap's demands assimilation phrases and rules of grammar. He never tried and probably knows even Harrap's. For someone who is part of the entourage of a publisher, he could be original. Note that this is the only negative comment on that date. Also note that I do not reject Assimil, I'm just saying that it's heavier qu'Harrap's and my preference - personal - going to the latter.