I just realized I've never actually seen on-prem Github. GitLab on the other side is everywhere, especially thanks to the Community Edition. I've never seen really big deployments, but for instances with 100-200 people on board there was never any problem (and DevOps guys sit right next to me, so I would probably hear something).

As for the hosted solutions, IMO both GitLab.com and Github.com are pretty slow. I've just recently started using non-premise solutions of both and Github slowness is really taking it's toll on my patience.