Speed is everything with these designs, the traditional helicopter has limited top speed due to the rotor inability to provide enough lift on the retreating blade as speed builds up, not to mention the less than efficient way of providing the forward thrust. Helicopters with wings and propellers can provide much higher speeds and utilise more of the engine power verses one with a tail rotor that has to sacrifice a significant proportion of power just to maintain directional control. Helicopters with two main rotors either in tandem, coaxial or intermeshing like the k-max can make use of all that engine power for greater lifting capability, but still they are limited at the top end as they still rely on entirely on the rotor for lift. Tilt wings and tiltrotors are far from perfected and date back to the late 40s in one form or another, even the only operational tiltrotor the V22 is not exactly new, just new to service. The Sikorsky X2 may ultimately be the right design, more elegant in concept and not even that new as the idea has flown before. The X3 has the advantage that is can built on to existing airframes, in theory at least, but I'm not so sure how practical it is with the props either side of the cabin which somewhat limits its utility. Ultimately bringing the main rotor to a stop and forming a fixed wing will allow the highest speeds, but they're not quite there yet. Interestingly, the Rotodyne concept improved and was a viable machine, we just lost our faith in yet another British innovation as with so many ideas that Britain generates. I wonder today if a modern version was available how it would be against the V22, that would be an interesting match. The idea ta least is still alive, see
http://www.groenbros.com/gyrodyne_tech.php
Also see
http://en.wikipedia.org/wiki/Canadair_CL-84 for some history on the Canadair Dynavert, I've seen movie of this aircraft and it really performs well even with guns, landing on a US warship and on the Whitehouse lawn in a bid for US order, but instead invigorating the US effort.