Which is best social media network?

Facebook and then pinterest are the two that I use the most.

Depends what you're using it for .

Facebook and twitter etc like mentioned above

Find it offline in your neighborhood. Improve it 10000x if you can.

1. Facebook - Is the simplest SN to monetize. Shoot I've done 5 Figures a month with 12 Catfish Accounts LOL
2. Twitter - So simple, pretty light on regulation enforcement. If you are only wanting to run a few accounts to make money Twitter isn't the place for you, but if you are willing to maintain 100+ Accounts be ready to bank.
3. Instagram - Has been the most strict in my experience, may be the most lucrative though ( I shall see in the next two weeks since I am setting up my first big campaign with big knowledge behind it)
4. Pinterest - Zero personal experience, but ive seen people do big numbers with 30 Accounts.

In terms of users or number of users - Facebook.
In terms of professionals - LinkedIn
In terms of sharing images - Instagram
In terms of short messages and following - Twitter

Facebook, Twitter and Instagram. Also Google+