you should always put your more "important" enchant on your main hand unless you're running around hit capped for more than one reason
like stated above, once you reach the hit cap to not miss with special attacks you shouldn't be focusing on hit... while yes, both of your weapons get the miss penalty, things like HS, WW, overpower... I think EVER execute (correct me if i'm wrong though) only take in the % to miss for special attacks, and all count for MH enchant proccing.
HS being the rage dump for all warriors (especially with the change to imp. zerker stance, you should pretty much NEVER be threat capped) that means that you should be using it fairly regularly... although that depends on your gear.
executioner IS the best enchant right now for a MH weapon to increase your dps. The most recommended one for off hands is mongoose, followed by potency.