Hey...
what do you think guys Which method is best for SEO?
1 Directory submission
2 Article submission
3 Forum Posting
4 Blog Posting
5 Blog Comments

well , i think here you are talking about back-links building , for me i think articles is best.But i want to say that SEO is not just back-links building , You also take care , of :
-unique content
-keywords meta
-url rewriting
-speed of your site (may affects) .

Now, I don’t consider myself an SEO expert by any means. However, I do have many articles that rank highly in Google’s SERP’s (search engine results pages). Therefore, based on my own personal experience and the success I’ve had with article syndication, in my opinion, the best SEO method is to create and distribute quality, relevant content.

You see, if you create and distribute quality, relevant content, your website will get linked to by quality websites. And if your website gets linked to by quality websites, your search engine ranking will increase.

Many techniques are there for SEO :

1. Forum posting.
2. Blog Writing.
3. Link Wheel.
4. Press Release.
5. Article Submission.

links building:
Social Book marking
Article and Press Release Marketing
Submitting your website link to high PR Web directories
Creating external Blogs with your website's link
Blog Commenting
Forum posting

I think that in SEO both on page and Off page techniques are important for site to get visibility and visitor on the website. But content present on site, title tag, keyword density in site, Article and Press Release Marketing, Do follow Blog Commenting
Forum posting are best techniques for SEO.