Again, this comparison is a bit misaligned, as OLED is a type of display technology, and 4K is a measure of resolution. You can have a 4K OLED TV, combining high resolution with the benefits of OLED technology. However, if you're comparing a standard 4K TV (without OLED or QLED technology) to an OLED TV (regardless of resolution), the OLED TV will usually offer better contrast and viewing angles.