Max Slashblast <- Allows you to mob monsters, thus train faster
Max Powerstrike <- 1v1 skill
11 Iron Body <- Reduces damage, saving pots. Not like pots need to be saved, but still...
Max HP Increase <- It's doesn't matter when you max this; you will end up with the same HP anyway. So do it last, you have more than enough HP
Generally in that order. HP increase is always last, but the first 3 can be chopped and shuffled according to preference. Just make sure Iron Body doesn't go past 11 unless you're both confident and desperate enough to take out of Slash Blast.