die Qual
agony / torment
Very great physical or emotional suffering; a state of intense pain or tormenting anguish.
Die ständigen Kopfschmerzen waren für ihn eine einzige Qual.
The constant headaches were sheer agony for him.

agony / torment
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agony / torment
Very great physical or emotional suffering; a state of intense pain or tormenting anguish.
Die ständigen Kopfschmerzen waren für ihn eine einzige Qual.
The constant headaches were sheer agony for him.

'Die Qual' (agony, torment) is the noun related to the verb 'quälen' (to torment). The whole word family describes a state of great suffering or pain.
Es quält ihn, dass er nicht helfen kann.
It torments him that he cannot help.
This word is very strong and emotional. It describes extreme suffering, not just inconvenience. Use it for truly terrible situations.
Das Warten auf die Ergebnisse war eine Qual.
Waiting for the results was agony.
The idiom 'die Qual der Wahl haben' (to be spoiled for choice) is usually used ironically or humorously. It describes the luxury problem of having to choose between many good options and does not mean real suffering.
In diesem riesigen Schuhgeschäft hat man wirklich die Qual der Wahl.
In this huge shoe store, you really are spoiled for choice.
suffering
'das Leid' and 'die Qual' both have to do with severe pain. 'Leid' is broader and can mean physical pain, emotional pain, or serious misfortune. 'Qual' emphasizes that the pain is very intense and feels tormenting. You say 'Leid' when speaking generally about pain or misfortune. 'Qual' fits better when someone can hardly bear something, for example severe pain, great fear, or a very stressful situation.

Die langen Schmerzen nach der Operation waren für ihn eine Qual.
The long-lasting pain after the operation was agony for him.
Viele Menschen zeigten Mitgefühl mit dem Leid der Opfer.
Many people showed sympathy for the suffering of the victims.