First you have to consider what each stat does for us
Stamina: Increases your health pool, allowing you to take more hits before dying. Generally, the only time you need to stack more stamina is if you're having trouble surviving a specific boss' burst damage. If you're taking too much damage outside the burst phases the solution isn't more stamina, you need mitigation.
Agility: Increases your attack power, crit rating and dodge rating. Attack power is more threat, higher absorbs on your Guard and (could be wrong about this last one) bigger heals on your Expel Harm and Gift of the Ox. Crit rating means more uptime on your Elusive Brew.
Expertise (15%) and Hit (7.5%): If your Shuffle timer is running low, you're Guard is almost off cooldown and your Stagger is approaching red but your Keg Smash misses or is dodged/parried you're about to take a lot of damage, eat through your healer's mana and possibly have to spend even more Chi on Purifying Brew than you'd like. The fact is Brewmasters are driven by their active mitigation. This makes them incredibly interesting and fun tanks to play but also more susceptible to lag, stuns and the need for their abilities to land.
Haste: Increases how quickly you attack and your energy regeneration. With more energy regen you can generate more Chi for your active mitigation. Quicker attacks means more chances for your Gift of the Ox to proc and more chances for crits to occur, increasing the uptime on your Elusive Brew.
Crit: Increases the uptime on your Elusive Brew.
Dodge/Parry: Increases the chance to avoid a slice of damage altogether.
Mastery: Increases your Stagger amount. Using Purifying Brew frequently, this could almost be viewed as a form of flat mitigation. When it comes to surviving high physical burst, such as a soft enrage, this stat becomes more valuable.
The second thing you need to do is to evaluate how ONE additional point of a stat compares to ONE additional point in another stat. All these stats sound great on paper. However, when you look closer at Mastery, Dodge and Parry you'll see that that adding a couple hundred points, for instance if you reforged 2 or 3 pieces of gear, you'll see the effectiveness of those stats go up by FRACTIONS of a percent. You can do that with your own gear and see how little a difference it makes, to evaluate the rest of the stats requires more math and spreadsheets and to compare all these stats requires some intense number crunching and tests and when it gets to that point, we usually have our trusted sources of information. So my best advice to you is do your research: find several lengthy, in-depth guides and compare and contrast them.