SHORT ANSWER
Start with Long Tong's Amber companion / element chain route
A coherent element and repeated companion events reduce the number of unrelated conditions a higher difficulty run has to satisfy.
“Best” here means the clearest fit for the difficulty's risk profile, not a measured universal tier. There is no verified DPS test that proves one Hunter wins every Nightmare run.
What changes at Nightmare
Exactly one third of owners clear it. Conditional pickups that need two or three things to line up start costing more than they return.
Choose one element and keep Amber active.
A Fire weapon, Dragon Breath, and companion or Fire support.
Check: The route should feel like one engine, not a gun plus an unrelated pet.
Raise companion event frequency.
Multiple Dragon Breaths, Ever-Burning Dragon Flame, Fire rate, and survival.
Check: If Fury is ending the run, take safety before another damage multiplier.
Use the element chain for elite and boss windows.
Element-matched relics, companion damage, and a reliable burst card.
Check: A second element is a last resort, not an upgrade path.
Boss and crowd priorities
Bosses reward sustained Fire pressure and Ever-Burning coverage. Use Fury as a finishing window and keep the weapon firing while Amber works.
Let Dragon Breath and spread effects handle packs while the main weapon preserves safe spacing. If rooms overwhelm you, choose coverage before the highest boss ceiling.
When the recommended core is missing
Keep the element your current weapon and relics already support, then prioritize companion uptime, frequency, and survival.
Do not: Do not hold an empty slot for one exact Fire gun while Amber is already contributing with another element.