In my opinion no tv is perfect the trick is getting a good compromise for the space. That being said here is my overview after owning (too many) TVs:
1) Size matters most. Get the biggest size you can afford up to a point. Be careful with panels above 70" or so, they can have issues with backlight uniformity and LCD Panels.
2) Backlight uniformity is very important, perhaps one of the most under-rated issues with TVs. So get a TV with the best back light uniformity possible. Some of the older "thick" LCDs are very good at this. Very little is distracting to the experience as having lighting affects that are unusual and notable.
3) 3D, HDR and 4k:
a) 3D blu-rays are still available, and many major theatrical releases are still in 3D. Most TVs are not able to deliver 1080p 3D passively, though some late LGs do.
b) 4k is very welcome on big format LCD and projectors or screens that you sit close to. The close dot pitch of the screens will make it look brighter and clearer even if you are not watching 4k content.
4k content is subtle but noticable when A/B tested against similar content (4k Blu-Ray vs Blu-Ray). The effect is clearer, more color, more lifelike images. It is not as noticable as the jump from SD to HD.
c) HDR is noticeable but not everyone loves it. It makes the directors vision more directly visible at home.
d) 120hz processing. 120Hz or 144Hz native screens are rare but a sign of a quality set. Good 120Hz processing will often be labeled as "240 or 480" etc. Very few sets will display 4k at 120hz interpolation and some early 1.4a HDMI sets are limited to 4k 30hz which may be good enough for watching movies if it is flexible.
Having a 120hz or 240hz set helps out with watching 24 or 48hz content, and sports. It can also help with streaming. Not everyone likes it but I believe having smoothing on helps content if indeed it is of high quality for example Sony or Samsung.
4) Curved screens feel natural and help with off axis viewing. It seems to me our vision process the world in somewhat curved realities. A curved screen helps when you have several viewing positions that are off axis and also when viewing the screen straight on by enhancing the illusion.
5) Smart tech. I would not buy a TV or not buy a TV for Smart features. Roku boxes are almost always faster and more seamless. And while rare it may be possible for their to be vulnerabilities in TV Smart code. I wouldn't even hook up your TV to the internet if it is a Vizio as they put out updates that can hurt TV performance (check out 80" M series circa 2013)
6) Exotic technologies such as OLED. Organic LED are very nice, they have some issues with blacks and need a lot of information to display properly. They can deteriorate so I would estimate usable life at 5-7 years. Looking at OLED PS Vita vs LCD Vita it is clear the OLED has beautiful colors that are deeper and more vibrant than regular LCD. OLED is more sustabtible to sunlight and direct sunlight.
It has been posited that OLED should be broken in on low back light settings and kept out of sunlight.
I would put curved TVs toward the end of the enhancements of the TV. If you can get a nice 70" for the same price it I would tend to buy it over a 65" curved.
