Since this thread specifically asks for comparison between the Oogie Boogie Bash at Disney's California Adventure vs Mickey's Not So Scary Halloween Party at Walt Disney World, here is my take.
We did
MNSSHP last October and were at OBB last night. The MNSSHP was better by a factor of two, in our opinion.
OBB had no fireworks nor a Sanderson Sisters/Oogie Boogie/villians stage show as is done at the MNSSHP. Those Florida stage/fireworks shows were about an hour long in total and came between the two parade performances.
The two parades were comparable, we thought.
The treat trails were comparable, but seemed to be easier to locate at the MNSSHP than at OBB.
It may have been our imagination, but last night after the first OBB parade, it seemed there was an effort to squeeze out guests, as many restaurants and bars closed early, as did many attractions. It could have been this was anticipation of thinning crowds, however.
All this doesn't take in to consideration the superior Southern California climate vs that of South Florida, or any other factors like hotels, or the other qualities of DCA vs WDW MK
I would recommend the WDW/MNSSHP over the DCA/OBB without hesitation. This opinion is based upon a single visitation of both parties over the course of the past year.