I was really happy to read this article by Kosta at BoardStudios - as it's nice to get a second opinion, especially when it confirms what I already believe. 

We've also tested all three, and in a very short summary, we found Quuu was the strongest for B2B content with a value audience, but both Taboola and Outbrain could deliver more volume. 

So it really depends on the objectives of your campaign. I do agree with Kosta that in the main Taboola and Outbrain are better positioned for a B2C audience, but I do feel the choice of which more depends on the network they advertise on, rather than the features of one versus the other. So it's worth testing both in a campaign to see which publishers work for you.