I have a question about wand

so I currently have magic missile imbued, a +1 wand of living earth and a base level wand of disintegration, i keep seeing people say to keep MM imbued for battle mage but is that always the best strategy? or would one of these other wand be better to imbue????

also does anyone know how to spend SoU on wands as im really bad at using them haha?

thank you