Full DET vs Full SS. It's either big heals or faster heals. Bigger heals=less over all healing=less MP usage. As a WHM its always better to have an abundance of MP especially in the situations where we might need to heal/raise a lot since its harder for us to regain resources and you can't always rely on Mage's Ballad since it cuts bards DPS, ~10% while its up, and sometimes you don't have one in the party.

SS is a stat that will only make a real difference in an abundance. ~25 SS=~0.03 sec. decrease. While arguably PIE doesn't make much a difference either, 33 PIE=~350 MP, still an extra Medica.

When possible I throw Aero(II) and even Holy to help DPS when there's downtime
More ACC=less misses


TLDR:
I want to be able to have big heals, extra MP in my pockets and DPS capability.