The most efficient way to de-orbit the satellite is to design it with de-orbit capability built in. Satellites already have maneuvering thrusters with propellant and/or "kicker" stages to maneuver them in their destination orbit. De-orbiting capability is just some extra delta-v onboard, and a de-orbit maneuver coded into the flight computer.
"Space-tug" like services from a third-party would be vastly more expensive. The only use case would to de-orbit a satellite that for some reason failed to de-orbit itself.
> De-orbiting capability is just some extra delta-v onboard, and a de-orbit maneuver coded into the flight computer.
It's not "just" some delta-v, it's the same amount of delta-v as the original perigee kick. Most satellites get their perigee kick from a booster stage from their launch vehicle that separates from the satellite and de-orbits.
Every gram of mass of fuel and engine on a satellite is a gram less of payload.
Yes, and it is still vastly more efficient to bring that delta-v with you than to use an entire other vehicle to come up to you provided by a third-party to de-orbit for you. Which is the case I was comparing and contrasting with in response to the parent comment. Evidently this is the case knowing that de-orbiting capabilities are built-in to many low-earth orbit satellites, although it (and any de-orbiting method) is prohibitively expensive for higher orbits
"Space-tug" like services from a third-party would be vastly more expensive. The only use case would to de-orbit a satellite that for some reason failed to de-orbit itself.