I just searched these very forums for wisdom mana formula and quickly saw the following thread.
https://www.project1999.com/forums/s...d.php?t=161975
It depends on level. At low levels, +mana items are way better. As time goes on, wisdom becomes comparably better and some pieces may grant more mana than whatever direct mana is available in the same slot. After 200 wisdom, there are diminishing returns. You have to do the math to calculate the difference between X wisdom and Y direct mana.