Both are very important in SEO. but from forum sites you will get traffic with back link.
--- Free Website Builder : Create a Free Website for Small Business | WebStartToday.com
Anything you can do to get a backlink to your homepage is beneficial to your SERP (search engine results page) results. The more links you have, the higher your site will be. And it will be genetic, or natural, and that's what you want.
---Joe Haffey, President Happy Brands Web Services www.happybrands.info
Both the works are necessary for the website promotion but from my point of view posting links through article will cause more better results than forums.
In my opinion both are important for quality back links,Article submmition in quality sites and forum posting in high PR forum sites make value high as compare to other task.
Both are good..but good PR websites is more important then this. Never create backlinks with the help of exact keyword anchor text.
Aarticle links and forum links ,blog commenting these are important off page optimization.