Forum or Blog
 

Which one is better for getting high rank on search engine?

Adding a blog or adding a forum? which will give more benefit?

It doesn't matter what you use to run the site, it's the content on the site that determine your rank (among other things)

A forum can be a great method of generating user-submitted content. However, that hinges on 1) attracting members and 2) members generating good discussion and not just spamming the place up with worthless junk. Too many forums wither on the vine. If you're confident you can attract good posters then I would say go the forum route - if not, then a blog may be the way to go.