I'm part of the Yarn core team, so my opinion is biased ;)
Overall both Yarn and npm are pretty good tools. We tend to ship more features, in part thanks to our community which frequently contributes, but npm isn't that far behind.
Plug'n'Play is currently exclusive to Yarn, though (Tink is quite different, I wrote an article about it not too long ago).
I found your text here, I will read it. :)
Since I wrote this article, I need to be opened for everything so I will test yarn thoroughly. It looks nice, starting by the mascot. :D
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