VIT all the way for all tanks, but GLA/PLD especially. Once upon a time there was a tanking meta for endgame where some points in STR was acceptable, but SE changed it in a patch so that VIT now counts towards a tank class's physical damage, to the same value as STR does, only VIT also raises HP and defense as well, so putting skill points onoy into STR would only end up costing you in survivability for no added gain. So put all your AP into VIT for GLA/PLD.