I'd look at a Dahon Curve mainly for its small fold.
It has flex in the stem but the small fold may be more important on a bus and it will be less intrusive at school.
Every folder is a compromise of rigidity, price, fold size, ride comfort, and weight.
I don't know of any bike that has all the positives.
In my opinion the perfect folder doesn't exist yet.

A full titanium or aluminum Brompton style frame, carbon seatpost and bars, 16" tires, carbon wheelset, Sram Red shifting, and Hollowgram cranks would be close to perfect.
Sadly it does not exist and even if the frame did, this bike would retail for $4000+.
Nice to dream though.