In my opinion, mp4 is more common (at least from a Mac perspective) but honestly it doesn't really matter. They are just container files for your content. 264 vs 265 is just about how data is written to the card (or whatever medium) and H265 is supposed to be a faster, more efficient way to handle your data stream. That's why the higher frame rates/resolutions are recorded in H265, it's more efficient (more compact file). The trade off is playback, H265 files are difficult for older machines (and even lower powered new ones) to play without stuttering, freezing, or stop starting because the compression algorithm is more difficult to uncompress on the fly.