So, if I understand it correctly: type I allows you to create all national units but only militia-level regional ones. Type II does the same, but without the elite national units. Both are expensive and bad for trade, but good for growth.

Type III allows allows recruitment of most regional units but only militia-level national ones while type IV allows no national units but all regional ones. Both are bad for growth but good for trade, and both have hapiness bonuses (one because of garrisons and the other because they are not truly occupied).

As I write this I realize this contradicts what Teleklos said, as he recommended against using type III or IV governements in underdeveloped provinces, but these governements allow faster growth, do they? I am just trying to figure out what would be the best choice for construction in a specific province.