It depends on your choice. Tyruntrum is a good offensive Pokemon, and Aurorus seems like defensive. But Aurorus has 4× weaknesses to Steel and fighting, so Aurorus sucks against them. Aurorus has 4 resistances and 6 weaknesses. While Tyruntrum has 5 resistances and 6 weaknesses. Aurorus has freeze-dry, which is also super effective against water and it has Refrigerate, that makes normal moves into ice-moves and let Aurorus receive stab and 30 or 20% boost power. Also, Snow warning let blizzard to 100 acc. While Tyruntrum has access to rock head, that prevents recoil from recoil moves, such as Head smash. Also, Strong Jaw works great, It make fang moves more powerful. And Tyruntrum can use dragon dance, that make Tyruntrum a powerful sweeper with Rock head or strong jaw.
I would prefer Tyruntrum. But remember that There are no better.