I find myself more similar to my four letter opposite. Assuming I've typed as INTP correctly, I find myself more like the ESFJ (4 letter opposite) than the ESFP (functional opposite). The ESFJ, even though it's the 4 letter opposite, shares all of the cognitive functions, just in a different order. ESFP shares the P but no cognitive functions. I'm very different from both of these types, but moreso the ESFP.
Since I've also considered other types, interestingly enough, I still relate more to the 4 letter opposite. If I'm INFP, I find myself more like ESTJ than ESTP. If I'm ISFJ, I'm more like ENTP than ENTJ.
I'm not sure if it's just me though or if others are like this as well. I do have a strong Si/Ne inclination and the types I've considered for myself are all introverts who 'use' Si/Ne.