Personally I used a 20/10 spec up until I started to do a relic reborn quest. 20/10 is good for leveling and such but once you start to get some decent gear from Amdapor Keep and such I suggest you respec and put everything into VIT. The attributes you gain from gear more then makes up for any short comings. Plus for fights like Titan HM and Bahamut's Coil VIT is far more important. 1% of Block STR and a hand full of extra enmity do you no good. An extra Flash in your rotation can make up for the enmity not gained from a 20/10 split.