I am an American native learning Chinese as my first additional language. I found Pimsleur to be marginally useful, but I am now almost done with Unit 1 of Rosetta and for me, Rosetta is much better than Pimsleur...

It really depends on a combination of things, such as your learning style, and perhaps which language you are learning.

One thing of note, is that Rosetta is more about the long haul. If you just want to learn a few conversational pieces it might be better to go for Pimsleur... Rosetta doesn't give you much you can use conversationally at first, it spends a lot of time teaching you things like "this is a girl" "this is a girl and her dog playing" and what not.

Also, if you used Rosetta v2, from what I understand v3 is leagues ahead of v2. I have no personal proof of this however, since I just use v3.

If you want to get somewhere approaching fluency without going to classes, I don't think it can get much better than Rosetta Stone + Flash Cards.