I think GitLab is a clear winner here since it's user friendly and designed for cross-functional team collaboration (GitLab dog foods their own product in all departments of the team, so you have HR, Marketing, Finance, etc all using it, in addition to the full product teams).
Pros and cons of dog breeding business
If you're having issues using GitKraken through a proxy, use the http.proxy Git config setting. Add your proxy to this file and give it a whirl. If that doesn't work, configuring remote.<name>.proxy might help. Bear in mind that local (repo-specific) settings override the settings your global Git config.