Guys... what is the best way to Lv up now?(please)

[Alberel]

Is this after you do it for myths or instead of?

It's instead of the myth reward. You get myth tomes if you do it as a level 50 or you get a huge XP boost if you do it as a sub-50 job. Personally I always make use of it to level an alt job every day as the myth can be easily farmed in other ways.