As of now, i'd say Wade because he has the greater NBA accolades, i.e. Finals ring and MVP, and has the demeanor and respect that would be a perfect face for the new generation of USA basketball.
However, the argument for Lebron is strong because of his more global exposure and the hype surrounding his rise to be the next GOAT.
Melo has a shot because, as was said earlier in the thread, of his commitment to representing the USA when so many superstars have placed it out of their priorities. In the first few games it seemed as though he was the perfect zone-buster and was acclimating perfectly to international ball.
Its a toss up if you ask me... i'd say maybe even Hinrich because he should be the starting point guard when he gets his confidence up, and his staunch defensive prowess.