AMR is pretty accurate. It may be considering the balance of stats it gives you as compared so something else. Often this means as other gear improves, that is best in slot in any given slot may change.
Askmrrobot is giving you the best in slot for the stat weights it has set as default, not what the community believe to be the best in slot trinket. Be very careful when playing with MR robot or other sites with pre determined stat weights as they are not always right, for example MR Robots default settings has the best in slot items aiming to net you 3k spirit not including procs 2k spirit is realistically the maximum you should need entering firelands with 359 gear and you should start lowering it there after.
Now with that said I used Rune of Zeth for quite a while the + crit is a nice chunk and if reforged you can still get a decent amount of crit and any other stat plus the on use +int is very nice when used with rapture and the 1 minute cooldown is quite low for a trinket with that much int on it.
Originally Posted by Antonne
What would BiS be? I'm currently using FQ and DMC:T.
That depends completely on what way you want your main stats, how you play the class, and what your roll is within the raid. Disc priest is a very complex class that can be spec-ed any number of ways and still get the job done but fallowing sites like Mr Robot force you into a build that may not suit your roll or the way you play.
If you could reply with your roll in the raid, 10 or 25 man tank healing, raid healing or support.
The way you play, combat logs with spell usage ( world of logs or other externally hosted log )
And and armory link to your character.
With those the best minds on here could assist you with your character in better detail.