I'm ENTP-A on this exam. I've always known I was ENTP, but I think when I was younger I came up type B.
MBTI and Big 5 aren't really that different. Perhaps the scientific community prefers Big 5 because it also evaluates Neuroticism? MBTI only has 4 factors. Either way, they are both built from the work originally done by Carl Jung.
Personally I prefer Strengths Finder 2.0. If a person really wants to know about themselves in a specific way, I find Strengths Finder to be the most specific.
They prefer it because it's a scale and not a binary system. Most people aren't really extrovert or introvert, but in between