Also, know this that if a blog is nofollow but has tons of people reading it and posting on it often, whereas another blog which is dofollow might be PR 7 but has NO readers or visitors at all, then your better off posting on the nofollow one, because you can expect more money from there.
However, if your planning on selling the blog, then more PR means higher price, so the dofollow one would be good and ideal for that