you basically want agi pieces with mastery on it with the second stat reforged to dodge. stat priority is: agi > dodge > mastery > crit = expertise > hit > haste.
gemming depends on what your progression is. if all you do is 359 raids then agi gemming is fine. transitioning from 359 to 372 raids you want mostly stam gemming to live through some of the heroic boss abilities. once you start getting 372 gear you can start gemming those pieces with agi since the extra stam is on the item now. an agi socket bonus is always worth picking up and using either mastery/stam or agi/dodge for meta activation is your best choice.