I'm going to go with INTP because I think it matters to them more.
I don't get the point of rating one type as being THE most intelligent. Each set of functions a person has makes them more inclined to receive and process information a certain way. This does not necessarily mean someone is incapable of receiving and processing information in other ways. To assume they can't is to assume we lack power over our minds, and perhaps we do--but I have yet to meet anyone intelligent enough to know that for sure. INTPs get information and judge/sort it differently from the way I do. If I stick to one rigid way of thinking, there are likely to always be things INTPs find that I miss, but it works both ways. I can and have used introverted thinking, but I don't like to. I don't trust it, prefer it, or feel comfortable with it. This is a limitation and probably a weakness, but I don't think it's something that can't be worked with. I'll probably never be a naturally introverted thinker or someone with an extroverted intuition, but it can't hurt to try and expand my mental horizons, and I don't think one person is necessarily more capable of training their mind than another.
I disagree that INTJs are more "in the box" and conventional than INTPs. The introverted intuition function we have can cause us to come up with some pretty outlandish theories (at least according to the people around us), but extroverted thinking sort of causes us to keep those ideas to ourselves in the face of what the world has decided is the logical precedent. My biggest fear is being delusional, and because I know I'm prone to it, I tend to trust in "truth" with witnesses backing it up, even if I acknowledge that truth is subjective.