Answers to this question vary by gender. Male INTPs typically say INFJ and female INTPs typically say ENTJ. That said, male INTPs have the highest statistical match with Ne users (in order: INTP, INFP, ENTP, and ENFP) and INFJs, while female INTPs have the highest match with NTs (in order: INTP, INTJ, and ENTP). That is, while female INTPs typically say ENTJ, when actual compatibility is assessed, they don't make the cut (which could make sense, as the attraction could be more physical/primal, rather than something based on shared beliefs/values/ethics and the psychological ease/compatibility it implies).
I also remember reading somewhere that in older age (30+), INTP males typically settle with INFJs, and INTP females end up with another INTP. Essentially, it was said that the males progressed from distressing/unfulfilling relationships with ISFJs or ENFPs, and that the females ended grew tired of dealing with emotionality (all INTPs have this problem, but I suppose social norms make it much worse for INTP females than INTP males) and just decided to settle with themselves.
As for me, it seems INFJs and ENTPs (and maybe INFPs) are the only types I'd "jive" well with in a relationship, though I'm not sure how the realities of being with an ENTP would play out (two procrastinators/perceivers where things need to happen), especially if children are involved. Either way, guardians and ENFJs are an absolute no. As in, no way! Never!