3rd row skills on wiki is not yet implemented on HK. Infinite Strength and Reversal Chance would have been good choices if they were. Currently we have maxed out Harmonious Spirit and Alchemy Mastery.
My thoughts on some of the skills....
1. Balanced Body - always active on dungeons, no conditions need to be met to use. Downside is that extra stats could easily be gained by upgrading your equipment therefore making this skill somewhat useless (3rd job armors give +phys/mag atk and hp as well).
2. Unleash Madness - faster increase in awake gauge could make you use awake mode for the entire dungeon run (works best with high awake duration increase stat). If I'm not mistaken awake mode gives you an extra 20% damage so this skill is good for massive attack increase.
3. Concentration of Magic Power - at max lv5 it gives 0.25mp so thats 1 extra mp for every 4 attacks you make. I've asked around for the effect of this skill if it would give 1mp at lv1 but it doesn't, yes it really does give a decimal point increase. Could be useful once we have henrir again.