People who say you should prioritize DH on MCH have no idea what they're talking about. The most beneficial stats are determined by the damage formula and stat spread on the gear. The best combination is usually found by making a rotational simulator that calculates the expected damage value for each gear set. Crit is the best scaling stat and as the patches increase available sub stats on gear sets, the priority for most classes will become, if it isn't already, Crit > DH >= Det > Sks/Sps. That is a broad generalization though, and specific priorities will vary based on class mechanics and available stat combinations on gear.

For machinist, you can take a look at this.