The thing you need to remember is they are all independent data sources and in some cases different companies. Their is no key to join them all up, you can only ever make assumptions that an individual may be the same person through personal information
It is entirely dependent on objective, you would generally use a mix of most of the tables, since you are looking at social media it is likely you are targeting customer profiling. QVSource has a couple of nice examples, I would suggest looking at them.
When I last used it to develop I found it best to pull all tables into a single dashboard (per application) and get an overview of each of the table contents. Once you have an overview of the data contents you can bend this towards your objective.
I personally use Mentions, followers, following, timelines, favorites