OLED TVs have the best picture quality currently available. If you're watching TV in a dark room, OLEDs can display perfect blacks, which enhance picture quality. They can't get as bright as LED TVs and have a risk of image retention or burn-in, although we expect most people to not be affected by this.
OLED TVs are said to have better picture quality, use less power, and have a much faster response time than LED TVs. But OLED technology is still relatively new, meaning OLED TVs are more expensive, and their lifespan has not yet been tested to match the 100,000-hour lifespan of LEDs.
OLED, on the other hand, has a better viewing angle, deeper black levels, uses less power, and might be better for your health. Both are fantastic, though, so choosing between them is subjective; QLED is the better all-rounder, but OLED excels when you can control your room's lighting.
We have a winner! In terms of picture quality, OLED still beats LED/LCD, even though the latter technology has seen many improvements of late. OLED is also lighter, thinner, uses less energy, offers the best viewing angle by far, and, though still a little more expensive, has come down in price considerably.