However with Crit Damage, you'll be using it from the beginning, each time you crit. And it carries over to your Summon as General Damage%. Unless you have an abysmal crit rate, you'll be doing much more damage over time with Crit Damage versus Berserk.
The only reason to get Berserk Damage as an Osamodas is if you never intend to hit an enemy directly with a spell or a weapon. In that case, yeah, it makes sense to maximize the stats that you send over to your Summon. But let's be honest here- you won't win much PvP unless you're dishing out damage yourself.