Blog in sub-domain or root domain, which is best??

[motionz]

It does not matter if your blog is in root domain or sub-domain to get ranked well. If you do proper content marketing along with on-page and off-page optimization then both can rank good. But, as you had said that your site contains multiple scripts such forum, customer contact page etc, so its good to create the blog in a sub-domain. Create a fine homepage and link your all pages from it, it will give the site a proper navigation and you will look good too in the eyes of the search engines.