For a mage Int > Arg > Spi, Cri == Dam

Main hand + Secondary usually have the same effect with a two-hand stuff on the
same leve, so mainly depends on the attribute. There is nothing like holding a stuff can cause more spell damage ...

What's your level now? I can recommended some weapons.

PS.

Cri = Critival Hit
Dam = Damage addition

Int = Intelligence
Arg = ... (forgot the word but is generally HP).
Spi = Spirit