The objective of the poll it is to share the method that better worked for you scaling positions on google. If there is a method that it is not here please share it ! There are others like classified sites, etc but the limit of the poll it is 10 options. PD: I apology if my english it is not so good, iam foreign.
Umm! How could the SEO effects be separated and studied, unless someone did so for research purposes? However, my knowledge says relevant backlinks from high PR pages and similarly relevant links from high PR pages will help you go up on search engines! Forum signatures and guest blogs will also help to the extent I know! But I will bookmark this thread to know what experts have to say!
For me directory submissions and theme sponsoring are working well. I think you've forgot to add option of "Theme Sponsor".
I prefer social bookmarking and article submissions are the best ones that generates more traffic to my site.
You can follow all method that you've mentioned because it's bit difficult to find which worked wonder!
It is best to get links from all sources. Most important it to have links from site's "on topic" than just on link farms.
I know some people might not beleive it but directory submissions do help with long tail keyword SERPs.
Directory submission has been my mainstay method for building 1000s of low quality links but blog commenting can be really great for getting links as well as making a network of friends.
Is it a mutlipule choice? So, if that is the case, then I guess, i will vote Article Submission. No duplicating things of course.
I will go for link exchange obviously non-reciprocal. Three way linking is the best way to get good result.