As someone who's used both Gitlab, Github Enterprise, and Stash in a corporate environment, I have to admit I prefer GHE, for the features it shares with core Github, if nothing else.
My only gripe w/ GHE is the lack of branch-based ACLs. If we want to implement a Github Flow (https://guides.github.com/introduction/flow/index.html) methodology, but also have automatic branch detection and testing in our CI (Jenkins/Bamboo/whatever), we end up having to assign all users the ability to create branches in the given repository (which, in turn, gives them the perms to push to master). I'm actually quite surprised that this hasn't been implemented yet in GHE; I can understand why GH wouldn't have it, but GHE (because of the nature of its user base) really should.
That issue aside, the UI in GHE is simply superior to GL and Stash.
I'm extremely surprised that Packer (http://www.packer.io) hasn't received more attention in the Docker arena. Its Docker builder, coupled with any of its provisioners, makes it a pretty attractive alternative to the simplistic layout and limitations of Dockerfiles.