Based on most min/max calculation(search around bluegartr if you're really curious) you should put your stat points for a tank job into VIT.

For most jobs it is best to feed the main gear stat, so yes STR for DDs is best.

In all honesty this whole system is sort of a dissapointment, they 'fixed' it from 1.x where everyone put everything into the two best stats, into something where everyone puts all their points into one best stat -_-.