OLED will have better darks and contrasts, is thinner and less power usage. QLED tries to imitate OLED contrast using smaller standard LEDs and and local dimming so it’s better than a standard LED but not quite as good as an OLED (thus not as expensive). The one time I’ve seen a QLED recommended over an OLED is for brightness, particularly if your tv is in a really well lit room.
In general the consensus seems to be QLED is close to good enough and significantly cheaper if you aren’t a videophile. If you are a videophile than it’s all OLED.