This is a simple benchmark. Take it with a few tons of salt.
For information, see this blog post.
Update:
Actually, I added a check against Play's Json library after @dyross suggested it in a Tweet. So it's really Spray-Json vs. Argonaut vs. Play Json in the "Just the Parser against a very simple JSON string" shootout. Yeah, it's really not a great "benchmark", but it suits me for what I'm looking for.
Parboiled2
In order to satisfy the parboiled2 dependency you should clone parboiled2 and do a publish-local on sbt.