Having used both there's more than enough in either that's bad to justify a switch to the other if you really want to. I personally prefer github's warts to gitlab's. In particular, I find that general site navigation on gitlab is quite tedious and it rarely centres useful information first. But that is very much a qualitative and not a quantitative complaint.
The main thing I find extra useful on gitlab is the ability to mark a MR as a WIP.
The main thing I find extra useful on gitlab is the ability to mark a MR as a WIP.