This paragraph from WDW Info sums it up for me:
First-time Disney vacationers should consider making their trip to Disneyland rather than Walt Disney World because it is a lot less intimidating of a resort. In Disneyland, you don’t have to worry about messing with the My Disney Experience App, booking your FastPasses in advance, and all the other confusion that comes with visiting Walt Disney World for the first time. Let Disneyland allow you to sharpen your Disney vacationing tools before you take on something more intimidating, because much of Disneyland comes fairly easily.
I’ve visited Disneyland once, and it was a quite different experience. With Disney World becoming more complex in order to maximize profits, Disneyland can be a quite relaxing experience. All fans should do this pilgrimage to Walt’s park once in their lives to experience how different it is from the Disney World craze.