OLED tv picture quality is better, no arguing that. LG makes all the OLED screens (even for Sony). The only negatives I’ve heard about OLED are burn ins, some pixels might age differently than others, it’s not as bright as QLED, and concerns on longevity because the technology is so new. QLED is better than the UHD. Older Samsung models have edge lit QLED. The Q9FN model (2018 version?) is the first one to to a full backlit QLED, which is better than the edge lit models as it offers more areas that can be controlled, offering more contrast, color control, etc. The 2019 model has more back panels than the Q9FN and offers better angled viewing. But comes at s price. FWIW I will eventually get a full backlit QLED because of the brightness and longevity. But OLED pictures are amazing. I recommend you look at each one by themselves individually. You will only see that the OLED is better than the QLED which is better than the UHD if you have them all side by side, which you won’t at home.