Subclass Certification Skills

With 4 certificates from the dual class, which skills would you choose and why?

I am tempted to choose casting speed but it looks like the most important would be pdef. Magic critical has a certain appeal too! :D

https://s32.postimg.org/pxj4l3dph/skillcertification.jpg (https://postimg.org/image/loeeixag1/)free upload (https://postimage.org/)

P.Def/M.Def - = Survivability
Atk Spd/Cast Spd - Casting speed on heals (not hard to cap cast spd, so maybe swap this for crit rate?)
P.Atk/M.Atk - Oly, more m.atk=more dmg

None of the boosts are all that great, but those are the ones I would choose and why.