I'd just gitlab because it's open source. You could run your own gitlab servers if you wanted. You don't have to worry about vendor lock in unless you use the paid features.
One of the nice things about Git is that it's an extremely portable data format, so vendor lock-in between Bitbucket, GitLab & GitHub isn't too big a deal. There may be a little project metadata that needs to be migrated using an importer, but your source code will always be inherently transferable. It's one of the big reasons Atlassian decided to partner with GitHub on Git LFS[0] rather than pursue our own solution: we didn't want to reduce Git's portability by creating multiple competing standards for large file storage.
We ended up with RhodeCode for internal repositories. It is open source as well, but in our case, security (we're a hedge fund) is critical. None of the other platforms were able to correspond to our needs.
Besides, RhodeCode has a nice community of developers: https://community.rhodecode.com
