I say AD, he can initiate, but building tank solely for that is just not very smart. He gets an extra ton of armor and magic resist when he uses his initiating move, and you should have more than enough time to flash away before that buff wears off. Malphite has the best initiation move in the game, but he is a less than stellar tank because none of his other moves make you really care about him after initiation, same goes for Urgot. His auto attacks still scale just was well as anyone else's and his Q makes it so you don't really have to build any attack speed to be effective.
I would always take a Shen or Amumu over an Urgot tank.