Kirk really is more efficient than Solo, isn't he?
I'm pretty sure that Han Solo would be able to be accepted on the Enterprise, because he oozes roguish charm, and that works wonders in the Star Trek universe, but he'd sell the Enteprise pretty soon, wouldn't he? Or he'd lose it in a bet?
Kirk, on the other hand, would be a fantastic asset to the Rebellion, and with his help, the Alliance would have been able to win the battle of Yavin with or without Jedi tricks. And I really don't think that the Empire would have been able to find the Rebels on Hoth if Kirk were calling the shots.