Despite the crap quality of the 90's flick, I actually thought Stallone was a good casting choice. He's got the right kind of chin for it. On the other hand, Urban is a bit of a geek god having been in such flicks (other than 'Star Trek') as 'Lord of the Rings' and the big screen version of 'Doom.' He's a pretty flexible actor and could surprise everyone.
Urban also got a decent chin in his own right and he has to given that one of the stipulations of the new movie is that Dredd never removes his helmet.