Me I would think 1st, 2nd and/or 3rd test (all 1st, 2nd, 3rd test quests).
Hardest Unpassworded 2.10 Regular LOZ Tile Quests from AGN QDB you played before?
Armageddon/James Quest or Hidden Duality Xtreme.
The Longest Journey, especially since I can't even pass the Patra room in level 4. (2 Patra Big Circle, 2 Patra oval, blue and red darknut, blue goriya, Pols Voice and a Like Like with 12 HC and no ring= true horror)