For most of my B2B thought leadership campaigns, LinkedIn proved to be a very effective tool. We also used Medium as a way to share content that needed to work through other channels. Usually we created programs that used a combination of the two.
My experience with Outbrain has been that it drives clicks, but most of that isn't qualified traffic. Little converted and it did not offer much by way of SEO, especially for B2B situations. That may differ when it comes to B2C.
A lot of publishers are now offering paid content as part of a general offering. There is no easy way to compare one publication to another in terms of pricing or results. I've done some research here and I'm happy to share, but overall you need to choose your channel and negotiate a deal.