I've used both of them among many other language programs.
Pimsleur is my favorite of all the programs I've used. This is because they actually explain certain things about the language. For example when I took the Japanese lessons it explained how some words in Japanese are assumed, like the words "I" and "You". Instead of saying "I understand" you would just say the word "Understand". It also explained how you can add "ka" on to the end of a word like "Understand" and it turns it into a question.
I used Rosetta Stone also when I first started learning Japanese. It is a nice program but it just wasn't meant for me. It actually got on my nerves because it doesn't really explain anything.
When it comes to learning some of the grammar of a language I used BYKI. You can find it at BYKI.com. I used it for Japanese as well as Finnish and it works really nicely for teaching you how to spell words and sentences and making them stick in your mind. It's also cheap which is always a plus.
I hope this helps.
~Flesh