We currently have a Jenkins setup and recently looked into both Concourse CI and GoCD as candidates for a change.
We decided not go with Concourse, because it has a complex setup with bosh. Not much other use cases are really covered in the docs other than a simple one machine setup so you are left to figure things out on your own (don't really have the time to go into all that, jenkins + ec2 plugin is very simple and just works). Also the minimal GUI, very CLI-centric. this is more of a particular thing, since I don't think that our current team will be comfortable with that UX and we have to weight this in.
We did like the docker-centric approach and specially the postgres backend that makes for a much more flexible maintenance story.
We decided not to go with GoCD simply because it feels very similar to jenkins in several aspects, but all concepts and workflow are different so we would have to relearn all that we do in jenkins in the GoCD way. Also redo all ops involved in backup, update etc. I just didn't find the killer feature to justify going through it. The postgres backend would maybe have caught my attention if it wasn't offered as an add-on for the expensive paid version.
In the end just decided to leverage more of Jenkins 2.x pipelines with shared libs instead of having independently configured jobs that are bothersome to maintain. Will probably make some changes to our agents to leverage more of docker instead of messing with AMIs.
Another major factor is the size of community, which alleviates a lot of worries.
As for Blue Ocean, I hope it evolves in the right direction, but right now it simply does not solve any problems for us. As said somewhere else, you can't build a pipeline with parameters. This is really a show stopper, parameterized builds are central to a lot jenkins use cases. Another problem is a single view for all jobs but no filter? The favorite jobs feature does not substitute either search or the view and folder way.