Some people don´t really understand how hulk "work" and how the change between Banner and Hulk work. Hulk is a complete different persona. Like Jekyll and Hyde, when one is in charge, he is in charge until he loses control. I will try to explain it:(sorry for my english)

In his early career, he was a new form of life living in a humam body, like a baby, and therefore could not control his emotions and banner also could not. The transformation goes wild, Angry > Hulk, Calm > Banner.

Banner

Banner was the first to understand this, and so, could stop himself from transforming. With this "advantage" over the hulk, he has now some degree of access to the Hulk´s powers without a fully transformation, but if he changes... the wheel is in hulks hands.

Banner was the first to understand his condition also, he is genius level, and started to think "where" he would go when hulk has the upperhand. This led to a "mind subspace" kind of thing, where they both exists simultaneously.

Hulk

With time Hulk also learns how to "stay in charge", this was first perceived when the "hulk wants to be alone" catch frase goes out. He is very dumb, and by himself he sometimes cannot even speak rationally.

He also can access some of the banners intelligence, and that is why he is sometimes a dumb goliath and sometimes he is talking almost normally.

When hulk became the maestro, or in every other "future hulk" story line, the situation is completely reversed. Banner is old and therefore cannot control his emotions, the Hulk is essentially imortal and is in complete charge of things, he is the one who, from time to time, let the banner in or out.

When Banner is dying, hulk stop letting him out, 'couse when he does, banner will die of old age and Hulk with him....

Mind Subspace and WWHulk

This struggle between then stayed pretty much the same, but in some aspects they completely agreed or completely disagreed, and when that happens they both experience a completely new form of interaction.

When they disagree completely, they "mind battle". This is the weakest form of them, when one suppress the other to a degree that the transformation is "forbidden" and there is no access to each others "powers" until the matter is solved.

When they agree completely they become strong. That is the WWHulk form. They where both betrayed when the Illuminati send Hulk to space. Only the hulk could survive in that environment, but the hulk consulted Banner for that. When Hulk foundCaiera they both fell in love, when the Hulk showed Banner to her, she kissed banner and that was the first time they both love and where loved by the same person.

When she dies, he is angry, but not "normal" hulk angry. They where both in pain, both angry, both wanting revenge...They where one single mind wanting the same thing using the combined powers of then both in it´s full potential.

Conclusion

That is why Hulk has different degrees of intelligence and transformation, ´cause they are not the same person, and they do not agree every time. When reading a story, try to put yourself in Banner´s and then in Hulk´s side, you will get what Hulk/Banner is in front of you.