Strength/Magic, Speed, Skill and Luck are the most important stats overall.
Tank units aren't actually so hot in a game where simply not getting hurt is more important than surviving lots of blows.
Str/Mag = damage, no way you can go without it.
Speed = doubling enemies (thus doubling damage at worst, tripling or more with damage skills), avoiding being doubled yourself (thus halving potential damage, being hit once for 20 is better than being hit twice for 15 each) dodging (avoiding damage altogether)
Skill = proc rate for many skills, critical hit rate (triples damage, more with skills and double hits) hit rate (reliability as well as superior critical hit indirectly, as to get a critical hit you need to get a hit roll in the first place)
Luck = proc rate for other skills like Miracle, evasion and critical dodge rates.
Meanwhile, HP, Defense and Resistance are reall bottom of the barrel in importance. You shouldn't be in a position to receive much damage in the first place, and if you are, dodging or triggering Vantage to kill the enemy before they get you is much, much more desirable.