Just guessing based on their technical inner workings:
For a single simultaneous user it is probably about the same, for multiple users on the same document Collabora might have a slight edge, for multiple users on multiple documents OnlyOffice will probably win by quite a margin (as it offloads much more work to the client PC).
P.s.: Etherpad will be much faster if that’s your main concern. See: Etherpad/Ethercalc with Ownpad is much better than people think!