After considering the question of who is the best critic, INTJs or INTPs, the correct answer is that it depends. The question is: what does it depend on? It depends primarily on what is being subject to criticism and the context in which it is called into question. Let's begin with the importance of context. I can picture an INTJ moving a fridge through an awkward doorway and an INTP sitting in an arm chair shouting instructions or criticizing how the INTJ is moving it. Most things in life are easier to look at objectively when you don't have a vested stake in the matter. Yet I'm convinced that if you put an INTJ and INTP in a similar scenario with two sets of rooms and doors to move the fridges through, the INTJ will do it faster and more efficiently. This is so because the INTJ is more likely to endorse an empirical/experimental/active approach than a rational/deductive/speculative one which is often more effective in a circumstance like this. It should be noted that due to a long history of Jness, the INTJ too could be highly critical as an outside observer. A difference, however, is that the INTJ is more likely to get up and help and/or show how it could be done more effectively. Thus, I think it can be broadly established that INTJs are more critical of ideas that have no basis in empirical fact. A history of INTJness affords them a library of experiences of what works and doesn't work which they are constantly drawing from and building on. However, their Jness is also a psychological bias that is conducive to goals and action but may result in the loss of greater objectivity. In other words, the indifference afforded by Pness gives INTPs the space to look at something comparatively more dispassionately than the INTJ. In certain affairs that are beyond the goals and intellectual interests of the INTJ, this comparatively more indifferent and dispassionate approach can be a source for better criticisms. On the other hand, the criticisms generating by Ne and Ti may not be as elaborate and comprehensive as those generated by Ni and Te. Thus, the sorts of criticisms are also going to be different. As an INTJ, I enjoy the criticisms of other INTJs since we're on the same page and, although working towards different goals we follow a similar process. Thus, any criticism that makes us more efficient in that process and more bulletproof intellectually is constructive criticism. Thus, ultimately answering who is the best critic depends on the criterion of what constitutes the best critic.