So which boost to prioritize?

It's been so confusing, at least for me.

We have elemental resist down, P/MAtk up, P/MDef down, elemental damage up, EW, P/M weapon boost (eg Cloud's fusion sword), P/M damage bonus (eg O Seph's kikuichimonji), elemental weapon boost (eg Seph's soba), elemental damage bonus (eg Yuffie's 2nd anniv shuriken)