to think: [transitive, intransitive] (not used in the progressive tenses) to have a particular idea or opinion about something/somebody; to believe something
Ex: Do you think (that) they’ll come? (we don't say: are you thinking they'll come)
to think: [transitive] (usually used in the progressive tenses) to have ideas, words or images in your mind
Ex: You're very quiet. What are you thinking? (It sounds strange if we say: You're very quiet. What do you think?)
So what are the differences between:
I think he might be good for us.
I am thinking he might be good for us. (Maybe there will have some pauses between "... thinking" & "he might...")