I'm assuming you're playing X and Y because of the tag you put in? Then Tyrantrum.
Aurorus is a disgusting Pokemon. One of the very worst Pokemon introduced this Gen; and its because of its typing. It has a x4 weakness to Wikstrom's Steel Pokemon and a weakness to Siebold, and its slowness means it's going to struggle to hit Drasna with its Ice moves before it takes a load of damage back. The league is also full of Fighting moves like Diantha's Goodra's Focus Blast and Siebold's Clawitzer's Aura Sphere, which are moves Aurorus will be knocked out from due to its x4 weakness to the moves.
Tyrantrum, however, has a very good Attack stat, a x4 resistance to Malva's STAB which Aurorus cannot offer and no weakness to Siebold's Water attacks thanks to its Dragon typing. It does have trouble with Drasna though - that is, if she uses a special move. Tyrantrum's Defence stat allows it to take physical Dragon moves and KO back. Its Rock moves knock out Malva easily, and Drasna's Altaria is weak to Rock as well.
Tyrantrum's ability in Strong Jaw is also more useful to it that Refrigerate is to Aurorus; there is literally nothing useful Aurorus can turn into an Ice move barring Body Slam, but Tyrantrum was Strong Jaw which means Crunch gets a handy boost which allows it to KO things like Wikstrom's Aegislash which is arguably the most annoying Pokemon in the league to take out.
Overall, Tyrantrum wins. Its movepool, ability, stats and typing are all better than Aurorus'.
