There's different reasons for all of these.
As far as my understanding, stamina is better because it's there all the time. You might avoid a hit xx% of the time, but stamina will always be there. You can only avoid physical hits, but stamina is always there.
People mainly stack stamina when they're doing progression kills for their guilds & maybe hard modes (which are probably progression anyway). It makes life a lot easier on the healers because the extra health gives them room for error.
As far as your stats, it doesn't look much different from others I've seen. 31k health sounds fine to me, depending on where you are. And if you're focusing on a melee boss, maybe the avoidance will work out for you.
In the end, it's best to have all sets covered for the boss you're fighting. Stamina, threat, avoidance, resistance, etc. Just like you would switch specs for a particular boss, so should you with your gear.
"Feel the fury of the mountain!" ~ King Magni Bronzebeard, Lord of Ironforge