How about a signature link from a niche forum?
I'm wondering though.. Zash is always ranking well for popular keywords while most of his links are coming from signature links only. At least that's what I read in another thread.
Maybe it isn't helping in rankings, but it might give some extra visitors ;)
Blogging are used in last.Actually it is done for the stability of your keywords.But any how it is considered the best strategy in SEO techniques.
Blog commenting is highly effected method of linkbuilding, Its upto you how you do it.
Though it will take work writing high quality comments, it seems to me that hanging out in a couple of hundred niche blogs could bring you more link juice and traffic than posting on forums. Blogs pick up a lot of traffic from Twitter , Facebook and Real Time search.
I suggest you to use back-links to get your keyword improved.
It is good to do blog commenting on .edu and .gov sites or blogs since these are trusted in Google. Through this you can increase your page rank easily.