Crit alone is not that great if you have to sacrifice a lot of MND for it, but if you can doubledip accuracy while getting crit up anyway, then it is pretty optimal. Of course, if you have items where you'll have the same amount of MND on both of them while one of them has crit and the other doesn't have crit - then go for the one with crit.
My own BiS varies per encounter, but for non-FCoB (ie. fights with no accuracy boosting needed) it's mostly max MND with max crit (accuracy ramped up as needed). For FCoB, my food-adjusted BiS per turn is as follows:
http://ffxiv.ariyala.com/PAGB - T10 SCH, food-adjusted (470 accuracy, 681 crit, 631 MND without party buffs).
http://ffxiv.ariyala.com/PAGE - T11 SCH, food-adjusted (485 accuracy, 685 crit, 626 MND without party buffs).
http://ffxiv.ariyala.com/PAG4 - T12/13 SCH, food-adjusted (515 accuracy, 673 crit, 621 MND without party buffs).
Each turn is adjusted so that I suffer minimal MND losses while having the absolute maximum crit, plenty of MND and VIT for whatever turn. Note: Demon Skirt of Healing and Dreadwyrm Tonban of Healing are more or less interchangeable if you don't need the VIT/mdef/PIE from the Tonban, but I just played around with the sets. (Demon Skirt of Healing is 5 MND less than the DW Tonban, but has 22 DET on it, meaning they more or less cancel eachother out, depending on whether DET weighs at 4 or 5 per 1 MND. It should be closer to 4 now as even with i110 gears, it seemed to weigh closer to 5 per. I will test around later though, not that much crit difference on the two anyway).
Note: these setups might change if the last upgrade of the relic goes up to i135 and if I find it worthwhile/easy enough to do just before the expansion hits (and it becoming pretty much irrelevant then). Up until then I am gonna get my accuracy elsewhere and will honestly be lazy with my relic. (Got my HA book before Novuses were a thing and could never bother with it, then Nexus came and I was still good with mah book seeing as we got the new books at i130/135. Now that the relic quest is nerfed up to Nexus, I might go for it on my downtime).