I prefer the Enneagram; it goes deeper and allows for healthy, average, unhealthy in a way that doesn't show up clearly, deeply, in MBTI: People tend to go for the 4 letters missing the functions.
That said, the book, Was That Really Me? by Naomi L. Quenk is excellent for delving deep into MBTI, especially confusing areas like inferior function, how INTJs and INFJs, for example, are similar yet confusing for people (F/J differentiation is not drastic), and otherwise contains a lot of information--and a way to put it together--for improving and accepting the use of one's dom and aux while not pushing the inferior function to the fore (to the point of exhaustion), and is a great resource.
Still, Beatrice Chestnut took the enneagram to a place that made finding my Enneagram and wing easy, and the why apparent.
I don't have to choose, however, so I use them both but don't mistake them as having the same purpose, e.g. enneagram was not intended (nor has it been skewed) to be used primarily for career choice, and that makes it (for me) more valuable in its scope.