An AWB is not politically popular at this time. It did cost Clinton dearly and most democrats are not eager to tackle this in the near future.
This is issue is one of the criticisms that I've levied against Romney. His statements made when signing the AWB as governor were simply wrong and alarming.
With that said, he's a smart enough guy to know that he will lose critical support if he takes that to a national level. Therefore I don't believe that he will lead an effort to reinstate an AWB.
Now contrast that with Obama. Obama has continued to make backdoor efforts to put the squeeze on the right to bear arms. His EPA goon squad is constantly on the attack. We've all seen the UN treaty discussions, which I doubt would be supported by our lawmakers. However he has demonstrated a desire to go after gun owners.
Of the two leading candidates, I think Romney would be the better choice on this issue. Of course, I cannot think of a single issue where Obama would be a better choice though