The wandering albatross, I believe. It is often larger than human children and lives out at sea, only coming to lad to lay its eggs once a year. It has the largest wingspan.
Although, it often contends with the title of largest with the Kori Bustard, which out-weighs the albatross.
I would double check my facts though~
(By the way, this is all assuming you mean largest FLYING bird. Otherwise, it would be the Ostrich.
