I think gnosis is a tad better than quartz since it updates MF ticks dynamically ( Unless quartz got updated and has it also in the meantime )
As Lazu said, I should've mentioned also that 14873 and 18215 have more or less the same DPS output, and there's just a difference in playstyle since 18215 is "smoother".
So depending on how much stats you lose to get the extra haste you should choose between 14873 and 18215.
Seems like I was wrong with my estimate on the way 2piece works :P Thanks Lazu