No need to compare, we are talking about reality.
If you tell me a particle traveled 10 feet, I know exactly how far that is.
If you tell me observer A views the particle as having traveled 20 feet, and observer B views the particle as having traveled 5 feet, then I know for a fact that one or both observers are wrong.
The particle traveled a specific distance, whether there is something to measure it against or not, regardless of how many different observations are made of the particle from different angles and distances in the universe.
And rest doesn't mean zero velocity, it means zero acceleration.