Orbi recently got a firmware update that added true mesh network capabilities, but from what I have heard, it is not quite ready for primetime.
That said, as somebody who sets up and supports residential mesh systems, Of the two mentioned, Eero has been the one that I have seen the most success and least issues with.
I have not personally set up or supported ubiquiti, so I cannot speak from personal experience on those, but I have heard good things about them.