on zerg comps you want to run Crit>master>spirit.. there is a fine line of how little spirit you want to have..every reforge goes into Crit. and mastery and spirit has to be balanced. thats based on how well you generally do w/ your mana
on caster comps or melee/caster you tend to have a preference. its iffy atm due to the new gear but i know for the most part ppl really enjoyed Crit over mastery. its preference. i choose Crit, i think crit this season will be even better due to higher stats. if you reforge full crit you should be along the lines of 36% with buffs. add the 25% crit from HS (61% total on HS) once fully geared. you should basically get a quick cast proc all the time.
but it should go Crit>spirit>mastery>haste or Mastery>spirit>crit>haste.
i always use the BM trinket due to the spirit it gives, it is the only trinket that we can use that adds +Spirit. spirit obviously adds mp5. when i do not use it i feel that i am always running low on mana towards end of matches.
i preferably use the Proc trinket and it is due to it being up just about 75-80% of the time. that is a pretty big buff. i feel that it is a better overall buff than what the on use provides.