Forum or Blog, Which One is Better in Terms of Revenue? Ur input will be appreciated.

Blog if you want instant money.

Forum takes years to grow, also it comes with lot of maintenance cost even if you are not making cash.

Blogs are easy to create, every one now uses wordpress, if you find the right nieche, you will make instant cash through ads

Depends on so many factors. You can't say which is better than the other.

Factors that come into play are subject-matter (and public interest level), your SEO strategy, your advertising budget (if any), and your online marketing strategy.