The Samsung Q90T is the best 4K LCD available. It has some issues unfortunately and it is overpriced, but in terms of PQ no HDMI 2.1 LCD beats it. It unfortunately still suffers from the Samsung plague of gimping the TV while in game mode but much less so than any other model at any other time. Overall - still the best LCD for gaming at 4K, if you care about HDMI 2.1.
See:
this post
as well as the avsforums dedicated thread to the TV.
Mind you, even the often lauded LG OLEDs have significant issues with Gsync and the like, as well as other issues, so it's not all rosy no matter the TV.
The Sony XH90/X900H is the best alternative to the Q90T if you want to save some money. It has good PQ, but not super bright, lacking some Sony processing magic, but maintains good colour accuracy & has that vaunted HDMI 2.1 port. The disadvantage at 75" is that they don't give this TV many more zones to keep up with the size increase, so it has better PQ at 55"-65".
LG LCDs are all crap, without exception & without fail, and don't warrant a purchase.
People recommending waiting for microLED have no clue what they're talking about. That's a decade away at best, if they figure it out at all. Right now it remains a technology for businesses that want to pay hundreds of thousands of dollars for giant displays - nothing more.
The LCD alternatives to OLED are almost here but still 1-2 years away from the polish they need.
- Dual Cell will get closest to the contrast ratio in the short term but in general they have processing issues taming both panels & the power requirements make it unable to get very bright. Will be decent alternative to OLEDs for movies - which is pointless.
- MiniLED are already here and widely available in the USA, but the problem is they are only in TCL TVs - which have crap processing and therefore can't tame the amount of zones & make proper use of it, so they black crush like crazy and have slow FALD transition times, plus they calibrate like crap. Once Sony jumps on board this train the situation will change and we'll have a very good alternative to OLED, and in many ways much better all while not breaking the bank. This is still at least a year or two away from happening, likely more. We will know more at CES 2021 in January.
So, to sum it up, if you can afford the Q90T get it. If not, the XH90 would be a good alternative. Can't really go wrong either way.