Not all links are created equal. You want to get a little of all of them. If google sees only article directories for backlinks this can be bad. You want quanity and quality. It looks unnatural to get 100 pr 5s get a variety. You forgot one effective method for backlinks and thats software directorys. Remember anchor text can give you a greater effect. I have ranked past pr 9 sites easily. But there backlinks werent for the keyword I was targetting. In my opinion the two from experience that get you the greatest and fastest results are using article submission software that spins the articles and submits to 400 - 900 sites works really well. And blog commenting but on high pr sites. One tip if you ever get a high pr link and you want google to find it quick ping it. Go to pingomatic.com and ping it too all the sites. You will see a good boost pretty quick sometimes less than a day doing this.
i think quality back links are important it doesn't matter from which type it is.. article , forum, profile...
all kind of back links are very important to your site getting nice page rank in Google.i think profile and article back links are helpful to you get nice page rank quickly.
forum participation, blog commenting, social bookmarking, article submission, link exchange, natural link building strategy
The best links are authoritative do follow links with a low number of outbound links. They can do wonders for any site!