Firstly, the method. The functions are not empirically verifiable, straightaway ruling out the possibility of MBTI being scientific.
Secondly, the MBTI company itself- the Myers-Briggs Company has funded all the research that support the theory, and additionally, the company has used the MBTI test to make $$$ for itself, disregarding constructive research on MBTI.
Thirdly, the creators. Isabel Myers and Katharine Briggs had no background in psychology.
Fourthly, it is unsatisfactory at times and fails to explain intertype relations and can be found wanting in details. Socionics however, is a much more detailed model and has concepts of Ego, Superego, etc that are highly interesting. Additionally, socionics has got an official type compatibility system.
Additional point: Many members of the online MBTI community are ignorant of the idea behind MBTI and use it perpetuate stereotypes about types, completely ignoring the idea behind MBTI- a model of the human psyche.
I wouldn't normally compare MBTI to astrology, but, if you think certain types are bad by virtue of being a certain type, you're no better than someone who says, "I don't talk to a Virgo", "Ew, I'm repelled by Geminis", etc and your understanding of MBTI is rubbish.
Moving on to other typologies, Enneagram personally I find more interesting, Big 5 is scientific but unsatisfactory, it doesn't have predictive power, being not much more than a list of traits.
Socionics is highly interesting, Temperaments doesn't get enough attention, and Instinctual Variants are FAR more important than the community gives them credit for.
My personal preferences: Enneagram>Temperaments>Socionics>MBTI>Big 5.
If anyone else is reading this, what is your stance on typology? Do you know your types in these systems I've mentioned here?
Any other comments?
Finis.