Your question really comes down to how you decide to compare one plane to another. One of the measurements you mention is wingspan. While this dimension is often used to compare overall size, it is generally not the most accepted measure. Aircraft are usually ranked by weight, the maximum takeoff weight in particular.
The An-225 is quoted as having a maximum takeoff weight of over 1.3 million pounds (600,000 kg). The FAI gives credit for a slightly lower weight of 1.12 million pounds (508,200 kg), the record set by an An-225 in 1989 for the largest mass ever lifted by an airplane to an altitude of 6,500 ft (2,000 m).
After pouring $7 million of his own money and another $18 million of government funds into the behemoth, Hughes only succeeded in making a single mile-long flight in 1947.
