I'd say the players..
The rest may have made genuine errors, that happens, football isnt a science, people get things wrong, Moyes doesn't deserve the sort of personal abuse dished out to him by the generals of this world. He tried his best and was found wanting. I thought he'd adapt his game at United, be more attacking to suit the ethos of the club. But I think he did his best and he comes across as a decent hard work honest guy who wanted to succeed.
But I think the players, Vidic and Rio especially, have damaged themselves by speaking out and just not being the same players. RVP too.. we'll see how it goes from here but whilst he may have made tactical mistakes a few players weren't putting shifts in like they did under Fergie.
Under Fergie no matter how badly we played we ran and ran, someone once said Fergie talent was making extraordinarily good players work harder than ordinary players, so even when things didn't go to plan we could grind out results.