Zaanse Schans or Kinderdijk?

The Zaanse Schans has more activities and is a short train ride from Amsterdam: 20 mins with several departures per hour.
Kinderdijk is more impressive. It is easily reached from the historical and under-visited river port city of Dordrecht with a direct ferry service, which makes it a special trip. Be in Dordrecht around 10.00, have a look in the centre (which is 15 mins from the railway station) and maybe a coffee before taking the 11.35 ferry service. Take the 13.07 service back to Dordrecht, giving you an hour at Kinderdijk.
Dordrecht is 1,5 hrs from Amsterdam with a half-hourly direct train service (in between a train with a change at Leiden).

I'd read Rick's description of Zaanse Schans before deciding, it's a mixed bag.

Just want to say - we def spent more than an hour at Kinderdijk. There was a short movie to watch, you could pop into a few of the windmills and look around (not that that takes very long). We didn't even walk to the farthest windmills, and still spent a few hours there. The only reason we didn't go to the furthest windmills was because it was really windy and cool and I wasn't dressed warmly enough (it was April tho).

it will take you more travel time to get to Kinderdijk than to Zaans Shans
There are other things to do at Zaans Shans.
We especially enjoyed the wooden shoe demonstration and the cheese tasting.
The working windmills were impressive also.
Just depends on what you want to do.

Kinderdijk is much more impressive and the nineteen windmills are in their working locations, not moved there like at Zaanse Schans. However, it is much farther away. We were staying in Leiden when we visited Kinderdijk and in Amsterdam when we went to Zaanse Schanse. We were disappointed in ZS.

You don't specifically say you are trying to get there from Amsterdam, but I'll assume that's what you mean. I did Kinderdijk from Rotterdam, off season when the ferry boats were not making the runs. It took me about an hour to get there by bus and I definitely spent way more than 1 hour walking around. It's huge, it's beautiful, it's very peaceful, you can get some phenomenal photographs and it deserves it's Unesco status. If you can rent a bike and really get out to many of the further windmills, I'd highly recommend it if it sounds up your alley.

If you want a more Disney-esque experience and you want it quickly, then yes, ZS is much easier to get to and you can eat cheese, see employees dressed up in costumes hawking wooden shoes and snap photos with them and learn something about windmills.

If all you want is a selfie in front of a windmill, you don't even need to leave Amsterdam. Go have a beer at Brouwerij 't IJ and immediately next door is a windmill. It is not open to the public, but it's nice to look at the outside of it looming over the brew pub while having a pint of a good local beer.

I think Kinderdijk is the more impressive site though there is more to do at ZS and it's close to Amsterdam should that be where you're staying.

Regardless, I think they're both great. How about this, if you are game? Should you find yourself in Dordrecht consider renting (or borrowing) a bicycle and riding the eight miles on table-flat land to the windmills at Kinderdijk. That'd be fun.

We plan on going to the Hague to see the MC Escher Museum, then heading to Delft to tour a factory. Could we then head over to Kinderdijk, or would we be better off doing Kinderdijk on it's own?

You'd make it all too rushed. Delft is too nice to limit yourself to a factory visit. Wander around in the centre, visit the wonderful Old and New Churches, and have lunch or an afternoon drink on the market place. Or finish your day in Schiedam, a few minutes further on the same railway line.
Making Kinderdijk a separate trip, you can combine it with Dordrecht, which deserves a few hours.

We went to Den Haag for Madurodam - just us two adults - and I was tickled and quite enjoyed it. We went to the MC Escher museum as well - hubby is more of a fan than I, but still enjoyed it.