There is no contest which of these rituals is best. Godspeed will always be the better choice in war. To make Onslaught more competitive, I propose the following for Godspeed and Onslaught...

Godspeed:

+15% Attack Speed
+10% Battle Gains


Onslaught:

+10% OME
-15% Combat Losses on attack and defense.
+10% Enemy Combat Losses on attack and defense


This would at least make it more of a choice which one to pick in war because currently there is really no reason to use Onslaught over Godspeed. Just my two cents.