Out of the rationals that I've met, I've only become close friends with INTJs. I think this has a lot to do with speaking a similar language and having the same orientation of world view. I dislike using functional analysis to describe relationships, but INFJs and INTJs are the only types with dominant Ni. This is not to say that sharing a dominant function is a requirement of meaningful friendship. I do believe relationships can be analyzed with functional analysis, but it requires full consideration to be considered to have any accuracy. Using the information I have now is like trying to tune a watch with a mallet and I believe the same goes for most discussions online concerning the topic. I believe it's more within our grasps to describe these relationships qualitatively.
I know two people are ENTP, one is my brother. We also speak a similar language, but I find that we reach the same approximate destinations in very different ways. Attempting to disregard any subjective memories I have of our conversations, he believes that there are no absolutes in the world (in terms of say "good" or "bad"). My worldview is different in that I believe the absolute is in the infinite forms and mixtures of, for example, "good" and "bad." (Bias disclosure: I believe my worldview is more reflective of the "organic" world we live in - the absence of "absolutes" is his worldview undermine his argument that there are "no" absolutes.) I also find that my brother is more interested in the art of debate (to the point of having an abrasive effect), where I'm more interested in it's application to the real world.
The nature of my relationship between INTJs and ENTPs are categorically different.