Well that depends on many different factors such as which school you are, are you playign mostly solo or with friends, which do you need more of, etc.
I have personnal found that the mana is much less important than health and stats. I have two death grands that I battle with in different ways. The one grand I took up through three different schools to get the shielding for that school and play him pretty much solo. I opted for higher hit stats across the board for that grand. The other grand I took up through the life school to the end and added the balance blades and traps and play him with friends to boost all other schools so that one I opted for the most health and shielding to be able to last longer in battles.
So you see it all comes down to how you want to play and what your basis strategy is.
