We used Github enterprise at my previous job, GitLab at my current one. The only driver - GitLab is free. GitLab is painful if you have a lot of experience with Github. Feature comparison is pretty similar, but then again a feature comparison with any SVN web interface is pretty similar too.
I can't pinpoint it, but I'm much more likely to browse, review, and offer pull requests in a github instance. It's intuitive and I'm used to it.