Forum is a platform where people assemblage at one place and exchange information to each other. Forum is more effective for your business because most of the people know about forum and come on that for information. From web promotional point of view you can visit that site and just login and put your link along with some good information.
Forum posting is one of the most effective parts to generate back link for your web page. The back link improves chances of achieving high page rank for your product page in search engine. One of the biggest advantages of forum posting is that you can get more traffic and lead for your business /service.
Some guide line for forum posting:
When you start to post forum for your business or product you should keep in mind that you cannot promote your business but you can just give reference related to your web page .Most forum have very strict rules related to add. If they seem that you are using forum for promotional purpose they block you and give you direct massage that you are doing spamming. When you post any forum first you can win the trust of that specific forum that you are not a spammer as well as try to put some good informational related to your service/product. Stabilize your identity as a reputed and expert in that forum.
Forum is best source for knowledge through discussion as well you can do one thing you can add link in your signature related to your business page.