SSME & Merlin use hydraulic actuators. For instance,
The engine is gimballed through two planes by hydraulic actuators for
vehicle pitch, yaw, and roll control. - Space Transportation System, Space Shuttle Main Engine Orientation, pg 4 (PDF)
and
Engine failure modes are minimized by eliminating separate subsystems
where appropriate. For example, the first-stage thrust vector control
system pulls from the high-pressure rocket-grade kerosene system,
rather than using a separate hydraulic fluid and pressurization
system. Using fuel as the hydraulic fluid eliminates potential
failures associated with a separate hydraulic system and with the
depletion of hydraulic fluid. - Falcon 9 Users Guide, pg 8 (PDF)
The Rutherford engine is generally believed to use linear actuators as gimbal actuators, but I'm having difficulty finding an official source. I'll update if I locate that.