It depends who you like. I think I would say Stewie, though.
No such character exists on Family Guy
There is a character named Lois in Family Guy.
The "coolest character in the world" is a matter of personal opinion. My personal 'coolest character' is Roxas from the Kingdom Hearts video game series.
There is no mailman character on Family Guy
Son
Meg
There is no existing Family Guy character 'inside' the suit. The Black Knight character is exactly how you see him.
Yes, he is the main character of Family Guy.
Jack and Kate are the two coolest characters in LOST.
Susie Swanson.
Edward!
The coolest guy around would be Harman Toor of Backwood heights, the 2nd coolest is Tanya Bains, the reason she is not number one is because she is a guy now cause of her stupid short hair.