Where you end up decides absolutely everything. Once you're in your host city, JET leaves you in the care of either a Board of Education (BoE) or with a contracting private school.
My situation had a very inexperienced BoE that took on way too many JET applicants and didn't know how to deal with all these foreigners. The JETs themselves were mostly fresh out of university and quickly started bullying one another as if they were back in high school. In addition, the JETs were considered subordinate to local ALT's that were hired 5+ years ago, who then began to have a management power trip over us despite having little to no training or experience as managers. A *lot* of problems came from one of those particular people, including sexist comments and workplace discrimination and harassment, yet our city's BoE did nothing.