Well I would put Mind as my 2nd stat no matter what now. It affects healing magic potency and the Flat Blade Combo, as per the 1.21 patch notes:

Flat Blade
・Combo bonus now affected by player MND rating.
・Enmity incurred by combo bonus increased.
Otherwise I'd say it's a toss up between STR and VIT for the top spot. One offers more damage, the other (theoretically) offers better survivability.