What was the key difference between the English and Spanish colonial systems?

The key difference between the respective colonial ventures was that the English settlements were established by private initiative. They were essentially commercial ventures designed largely to expand trade and exploit raw materials. English colonialists still had to obtain formal permission from the king to establish their new settlements—such as the London and Plymouth Companies that founded Jamestown, for example—but they shouldered the burden of the enormous financial risks involved.
With the Spanish, it was different. Their colonies were supported, financed and supplied by the Crown. As such, Spanish colonialists were never in any doubt that they were still subjects of the monarch no matter how great a distance they were from the mother country. English settlers, on the other hand, though professing loyalty to their king and his laws, enjoyed a greater degree of freedom in running their own affairs.
The Crown's initiative in the project of Spanish colonization was one of the main reasons why Spanish colonies in North America did not allow immigration from outside Spain. Political authority in Spain's colonies closely mirrored the system back home—a top-down structure in which power was concentrated in the hands of an aristocratic elite, dedicated to serving their monarch.