Tilt rotors (e.g. Boeing V22 Osprey) and thrust vectoring system (e.g. the Harrier Jet) use the same rotors/jets for vertical take off as for forward flight, tilting or re-orienting them from a vertical position for hover to a horizontal position for forward flight.
However, similar to a car, efficient vertical take off and hover is best achieved in first gear, which means large, slowly spinning rotors (more torque, less speed), while efficient and fast forward flight is best achieved in seventh gear, i.e. small, fast spinning rotors (less torque, more speed). Large and slowly spinning rotors translate into more efficiency, less fuel consumption and importantly, much gentler down-wash and less noise during hover. For forward flight however, large rotors are a problem as they create a lot of drag standing in the wind. Small, fast spinning propellers (or jet engines) are more efficient and effective for fast forward flight.
Tilt-rotor systems are a compromise. Their rotors are too small for efficient hover, and too large for efficient forward flight. Although they can do both, they can do neither that well. This translates into slower forward cruise speed, larger fuel consumption and very large down wash as well as noise during VTOL. As such tilt-rotor systems can very likely at most utilize airports and perhaps helipads, not however the vast number of other potential take-off and landing sites available in commercial and residential areas, somewhat defeating one of the main purposes of civilian VTOL systems.
A transformer system using large rotors for vertical take off and hover, and small rotors for forward flight can do both, hover and forward flight, better than a tilt-rotor system.