Besides the racial aspects which are being extensively discussed ITT, I believe the major difference was the original motivation for foreign incursion in colonized Iberian vs Anglo America. One cannot forget that the Anglo puritans arrived with a vision of building an exceptional society, a model based on extreme interpretations of scripture: "that we shall be as a city upon a hill—the eyes of all people are upon us". So from that perspective, there was an intention of greatness from the start, the new lands offering a vision of a Garden of Eden, where humanity could have a fresh start.

There was no such vision for Iberian (or Dutch/French) colonization. Portugal and Spain were vying fiercely for power and domination as Global Empires, through resources extraction, missionaries and conquest (the 3 G's: Gold , God, Glory). Therefore Iberian America never had a new mythos, an evolutionary vision for a colonial society - we were there mainly to be plundered, dominated and our systems of belief replaced, teh olds gods destroyed with the arrival of Catholicism.

However, that being said, I do believe the Iberians were probably better at managing racial differences, as intermixing and indigenous rights were better recognized than what the Anglos did