If you can, you might want to try a demo of Rosetta Stone before you take the several hundred dollar plunge. Some people really like its teaching style, and some people don't. I tried it out (Spanish version) a few years ago, and I personally didn't like it at all. Many people love it and it works great for them, though.
In any case, I think Memrise would allow you to learn and retain vocabulary at a much faster rate, since the words are accompanied by mnemonics that give you tricks for memorizing words. At my peak, I was learning about 50 words per day with it, with fairly high retention (answering about 80-90% of the words correctly the next day)... so if there's any one piece of advice I can give you, it's to try several methods/programs to see which works best for you. Learning vocabulary via brute force methods-- just hearing it a few times and hoping you remember it, as most programs teach it-- was one of the slowest methods I tried.