When downloading videos, I have found 720P to be pleasant to watch. Rarely are higher resolutions available, nor helpful, and my 5K monitor is a multiple of 720P.
Standard Definition, tube TV's, are 480i, therefore many of the cheap channels broadcast reruns in 480p or 480i. They look terrible. I assume that reruns are limited to this resolution. Most of them were recorded on tape which is 480i.
Some shows, like Star Trek The Next Generation were recorded on film and therefore capable of higher resolution, but not Star Trek Voyager.