Generally best ratio in main hand since it swings more often and later (level 28+) has a damage bonus while the offhand doesn’t. In certain situations the damage bonus and speed will make up for lesser ratio weapons. It’s why the Wurmslayer holds up ok for a while but gasses out in the 50’s.
Here is the damage bonus chart:
https://lucy.allakhazam.com/dmgbonus.html?setcookie=1
In short, go 6/28 MH and 5/24 OH. They are a negligible difference in ratio (2.5% difference) so it likely won’t make a materially difference.