Nofollow prevents the passing of PR. It still counts as a valid backlink which is crawled. Noindex prevents a link from even being crawled.
I recently read a great study that concludes, nofollow links can pass link juice when dealing with very specific linking text. Linking text with nofollow was shown to increase rankings for very specific keywords in the linking text. The author concluded, commenting on nofollow blogs was an effective way of increases search results for keyterms closely related. Best of luck!