Trials: Do high tiers, gold give better loot?
According to the event description, higher tiers give you better loot.
The loot drops from the mobs randomly while you kill them, no reward at the end, so how well you did doesn’t factor in to the loot bags. The only factor I can tell is the tier level. The loot bags are also not like WvW bags from kills, but more like chests, so I don’t think magic find affects them.