Been a while since I did my research but as far as I know OLED will have superior image quality overall, and some people confuse Burn-in with Image retention. Burn-In is permanent and as long as you don't do something crazy and have some screen savers that turn on after inactivity, you should be fine.
But I've read image retention can happen on OLED, like the HUD from your previous game might still show signs when you load your next game, but will disappear after a few min....something like that. Anyways, I've got the KS8000 and I'm quite happy with it, QLED is like the successor to that and it's better overall, closer to OLED quality but OLED is still the best picture quality as far as I know.....however while OLED has overall better image quality, it's not better in every single category and you can read up on some review sites to find out more differences. I've read people complain that OLED doesn't seem as bright as LED for instance, that's probably more about preference than anything though.
OLED has a lot better image quality for a good reason. I will explain. QLED is just LED. The exact same technology. They call it QLED to make it seem comparable to OLED. Here is the main reason it can't compete with OLED, the backlighting.
With QLED, you have divided zones in the back of the tv that can be turned on and off on any given scene. It's called Full Array Local Dimming or FALD. During a scene that has dark and bright areas on it such as bright lights during a night scene, the zones in the dark sections can be turned off while the ones that affect the bright part of the screen will be turned on giving it a lot better contrast. Of course this has it's limits due to how many zones the TV has and how well it is implemented. The best LED tvs usually have something like 100 zones, sometimes you get pretty good results with less zones. For example, the Sony 900E has 40 zones if i'm not mistaken.
With OLED, each individual pixel can be turned off or on at any time. So in effect with an OLED you have over 8 million pixes and "zones" that can be individually lit to best represent that scene. As you can imagine it is vastly superior to LED.
The advantage of LED comes when you put your TV in a bright room and that causes of course the screen to look washed out or maybe there are reflections on the screen. When you have that situation you need a lot of internal brightness on the TVs part to offset that. That's where LEDs come in. In very bright rooms they can get super bright to look good. OLEDs don't get as bright so in very bright rooms, the QLED or LED will look better.
At night or in dark rooms there is no comparison. OLEDS are just vastly superior.
As far as burn in is concerned it is a small problem with OLED TVs. However, if you don't go crazy and just leave a static image on it all day and night you shouldn't have any problems. I would recommend an OLED for movie watchers and gamers. Even heavy hard core gamers that do a lot of gaming, OLED is the one for you as long as you can afford it. What I wouldn't recommend is using an OLED as a PC monitor. Right now I wouldn't go that route. If you want to do that just get an LED. My two cents.