Alright, I know it gets overdone, but I personally never get sick of comparing them.
I know we almost all would agree WDW is the better vacation site to bring a family in general since there is more to do Disney-style, but if you isolate just the flagship park Disneyland and Magic Kingdom which park is better, and why?

Magic Kingdom has the scale…but…

Disneyland has the Magic!

I have been to Disneyland and Disney World several times.

My opinion is Disneyland is better then the Magic Kingdom.

Smaller Park = Less Walking with more Rides and Attractions better thrill attractions and generally better versions of the same attraction.

Less stressed out crowds Disneyland is seen more as a locals park not a once in a lifetime visit for most people.

Better Night Time shows.  Fantasmic is awesome at Disneyland.

Opening Day Attractions
 nine opening-day rides still in operation to this day.  I love nostalgia.

And better the availability of characters, and unique ones at that, in Disneyland.