For reasonable bitrate/resolution pairs, both matter. Clean 1080P will beat bitrate starved 4K, especially with modern upscaling techniques, but even reasonable-compression 4K will beat good 1080P because there's just more detail there. Unfortunately, many platforms try to mess with this relationship, like YouTube forcing 4K uploads to get better bitrates, when for many devices a higher rate 1080P would be fine.
I'm curious, for the same mb per second, how is the viewing quality of 4k vs 1080p? I mean, 4k shouldn't be able to have more detail per se in the stream given the same amount of data over the wire, but maybe the way scaling and how the artifacts end up can alter the perception?
If everything is the same (codec, bitrate, etc), 1080P will look better in anything but a completely static scene because of less blocking/artifacts.
But that’s an unrealistic comparison, because 4K often gets a better bitrate, more advanced codec, etc. If the 4K and 1080P source are both “good”, 4K will look better.
