I have substantial experience with Pimsleur. Whatever you hear about "unnatural" sentences you won't need to worry about at this level. You will get very good pronunciation from using Pimsleur. In fact native speakers will mistake you for having a better command of the language. That's what happened to me. The problem is they will talk too fast to you and expect you to know things that you don't. I met many people who were learning from just a book and their pronunciation was so bad that I couldn't understand how native speakers could understand them at all. I don't know anything about the other one Michael Thomas.
EDIT: I just heard some of Michel Thomas lessons....... They are not for at all. I much prefer Pimsleur.