If you're happy with your TV, keep it. But if your TV is getting old and you're curious how much better modern TVs are, this guide should be able to help you out.
What we've done is break it down by type and age of the TV, and given a recommendation about whether you should consider upgrading.
Should you upgrade at all?
Generally speaking, if your TV works and you're happy with it, don't worry about upgrading.
We're a long way off from the majority of TV shows and movies being in 4K resolution, let alone high-dynamic range (HDR), wide color gamut (WCG) or any other widespread change in content that would "require" a new TV. If and when those things happen, 4K TVs will be even cheaper than they are now. And they're pretty cheap already.
Even without 4K content, however, buying a 4K TV now makes sense if you actually do want to upgrade. One reason is because 4K TVs usually deliver better picture quality, with any source, than non-4K models (for reasons that have nothing to do with resolution). This is especially true with HDR models.
So, if you have a...
LCD without local dimming: Maybe upgrade
Most LCDs more than a few years old don't have local dimming, our favorite picture-enhancing feature for LCD TVs. It allows the TV to control brightness in different areas of the screen. Modern LCDs with local dimming will look more real, have more apparent depth, and have more "punch." The top of the line models will have HDR and WCG, which can look really amazing.
Depending on the age of your current LCD TV, and of course what 4K TV you end up buying, the difference may be significant. Of all the categories of TVs we're talking about here, this is one of the ones I'd be most likely to recommend upgrading from, especially if you're looking for something larger.
If you step up to OLED, the difference will be profound.
LCD with local dimming: Don't upgrade
With few exceptions, local dimming LCDs look pretty good. Most of the ones with a full-array (as opposed to edge-lit) local dimming look pretty great. Many edge-lit models look good too.
True, the HDR and WCG capabilities of modern LCDs will make them look a bit better, and OLED even more so, but the difference won't be as significant as if you were upgrading from some of the other TVs on this list. Generally, I'd say save your money.
Plasma TV (2008 or newer): Don't upgrade
This is especially true if you still have a Pioneer Kuro or one of the last Panasonic or Samsung plasmas from 2012 or 2013. These later generation plasmas still look fantastic compared to most LCDs. Sure, OLED looks even better, but they're still a lot of money.
Once HDR and WCG content becomes more commonplace, then an upgrade is worth considering. Until then, enjoy your awesome TV.
Plasma TV (2007 or older): Maybe upgrade
Again, if you're happy with your TV, keep it. The older the plasma is, the less it holds up compared to modern TVs. LCDs with local dimming will certainly be brighter than old plasmas, and might even have better contrast ratios. LCD's motion blur might be acceptable (depending on the refresh rate), though off-axis (how far you can sit off to the side and still enjoy the image) will likely be far worse on a modern LCD.
The closest comparison to modern TVs will be OLED, but again, they're pretty expensive. So I could see this going either way. A new TV will certainly "wow" you, but your current TV is probably pretty good.
Rear-projection TV: Probably upgrade
I'm surprised you're still able to buy lamps for your TV. Most new LCDs and OLEDs will be far brighter, and have a better contrast ratio than just about any RPTV (CRT models excepted). If you have a DLP-based model though, the motion resolution on it will be way better than an LCD or OLED.
CRT 'tube' TV: Probably upgrade
I'm impressed with your ability to keep a TV running, but modern TVs will be bigger and brighter, OLEDs will have a better contrast ratio. If you ever need to replace your Blu-ray player or media streamer, most of the latest models only have HDMI (which your TV probably doesn't have).
Front projector: Don't upgrade
If your projector is from the pre-3D era, new projectors are likely a lot brighter. Unless you're really well heeled, they're still just 1080p though. If you're really feeling the itch to upgrade, I'd recommend getting a new projector over a 4K TV. In fact, getting a new display that's smaller than your current display is almost always a bad idea. It will see so small, especially compared to a projector.
As usual when someone asks, "Should I get a new ___?" the best answer is "It depends on what you already have."
By the way, if you're thinking of upgrading the size of your current TV, that's worth considering. I don't think I've ever met someone who regretted getting a larger TV.
Though many of us were worried that TV picture quality improvements completely would stagnate with the death of plasma, TVs, especially thanks to HDR and WCG, keep getting better. After all, even I say 4K TVs aren't stupid anymore.
Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED, why 4K TVs aren't worth it and more. Still have a question? Tweet at him @TechWriterGeoff then check out his travel photography on Instagram. He also thinks you should check out his sci-fi novel and its sequel.