I see that blogpost are permanent and doesn't cost that much. and blogroll makes sure you are on the page which has a good PR but you have to pay it monthly. so how do you value the differences?
I wouldn't pay at all if I was you, when you can get placement like that for free buy doing seo and marketing the right way. Plus if you are not on at least 1000 of high PR sites..it will be an waste of time...