Q: Why is expertise better than hit? When should I stack one over the other?
A: 33 hit rating translates into a 1% increased chance to hit while 33 expertise rating translates to 4 expertise skill, which is a 1% reduction in the boss' chance to both parry and dodge. This means that up to a skill of 26 (at which point dodges have been eliminated) expertise is effectively giving you a 2% increase in your chance to hit the boss from the avoidance reduction. Past 26 expertise skill, both stats will give you the same increase in TPS/DPS, but expertise will continue to reduce parries, which reduces the chance of a tank gib, making it a superior stat to stack until you reach the "cap" of 57 expertise.
Just remember that Taunt uses hit rating so don't neglect it completely. You might have problems <100ish but 150+ hit I've not had issues.