Tanaan - Rares have a short spawn timer and are lootable once per day.
Pros: Easy to target a specific rare, allows progression items (e.g. shipyard blueprints) to drop from rares
Timeless Isle: Rares have a long spawn timer and are lootable each time they are killed.
Pros: Rare-hunting can be a long-term activity, encourages coordination
It looks like we will be using the Tanaan style going forward (https://twitter.com/Muffinus/status/639487827034574848). Which do you prefer?