OLED TVs have better picture quality than LED TVs (see our OLED vs LED TV comparison). However, they are very few of them on the market right now. In North America, only LG (the only real OLED panel manufacturer) sells them. LG has announced new models at CES already, but they're still a few months away from being available.
Best OLED TVs
The LG E6 is the best flat OLED TV that we tested in 2016. It is not only 4k, but it also supports HDR. It is currently the highest rated TV on our website, and it beats the LED TVs by a fair margin.
There is also the G6 that comes with a more powerful speaker system, as well as a 77-inch size. The picture quality isn't better, though, so stick to the cheaper E6 unless you want a 77".
The LG B6 is the cheaper version. The picture quality is about the same, which makes it a better buy for most people. There are only two main things lacking: 3D and the better sound. It also has a slightly higher input lag, but it shouldn't be an issue for most people.
Most, if not every person, should buy this one (or the C6) over the E6. No picture quality advantage comes with the higher price. Only a different design and better sound. The price conveniently dropped from the stratosphere before Black Friday, so while still expensive, it's a bit more reasonable nowadays, and a definite recommendation for those looking for a high-end 4k OLED TV.
Currently, only LG sells OLED TVs in the US, and they all have relatively the same picture quality. Other manufacturers should start entering the OLED market in 1-2 years. Some manufacturers like Philips and Panasonic have produced some OLED TVs that use LG panels, but these aren't sold in North America.