Which Fare Portal Provides cheap and best Air Tickets.

If you can figure that one out you'll be a millionaire. If I recall what my wife told me while she was working as a travel agent, most airlines have price that the airline decides. The company can sell them for less and lose money on the transaction, but most just use what they get. If you want to figure that one out, you can find a list of them and go through for the specific flight you want and compare it over the different sites.

Check them all, I use Kayak, Expedia and the airlines.

Impossible to answer. Prices vary by date and destinations and starting places, and time, and so on.
Some of the online sites are buying each other out so it will be easier.

Sits back and waits for the "helpful" link to arrive ;)