I voted "a mix of the above" because there are different sets of dungeons too.
The loot at the end must be something according to the place. I mean, in a dwemer dungeon you expect to find jewels, old dwemer clutter and dwemer weapons/armor.
In a daedric you expect to capture very powerful souls for your enchantments and get that awesome daedric katanas or daedric weapons.
In the sheogorath region you expect to find aureals and ebony equipment and their powerful souls if you kill them.
A modded dungeon must reward what it fits more for that dungeon. If it's a tomb, the player can expect to find some unique armor, weapon or jewel. But, alas, there are many types of tombs too.
If that one has been raided by bandits, you'll find bandit loot and according treasure... and the chief of bandits himself should wear some piece of unique armor if he is a warrior, and some powerful scrolls and a unique robe if he is a mage.
What I'm trying to say, it's the loot has to be according to the place and its actual inhabitants. A modded dungeon needs lore and a story, then the loot it's easy to decide