Mart,
"Tiltrotor will never be as efficient in hover, but counterrotor is unlikely to be as efficient in high speed flight."
They both have latterly located counter-rotating twin main rotors. The concern is; which configuration can significantly improve high-speed flight without jeopardizing hover (payload).
The primary differences between the tilt-rotor configuration and the ABC-rotor configuration are the means of propulsion and the means of lift.
Tilt-rotors ~
~ Hover ~ Uses the rotors.
~ Forward flight ~ Uses the rotors (props) for propulsors, and separate wings for lift.
~ The prop/rotors are not ideal as rotors nor are they ideal as propellers.
ABC-rotors ~
~ Hover ~ Uses the rotors.
~ Forward flight ~ Uses separate props for propulsors, and the rotors as wings.
~ The ABC-rotors are not ideal as rotors nor are they ideal as wings.
For reasonable fast forward flight, my money is on the ABC-rotors over the tilt-rotors.
For very fast forward flight, my money is on Reverse-velocity-rotors over the tilt-rotors. It will be a lot easier to produce a craft with reverse-velocity-rotors and fan-jets then trying to morph the tilting rotors into fan-jets during transition.
The next question then becomes Coaxial, Interleaving, Intermeshing or Side-by-side?