RX100 video newb needs advice please
AVCHD was created as a means for movie file storage, but is not universally compatible for playback. mp4 is much better suited for playing on almost any device. Both use h.264 compression so there is software/ freeware available that will convert one to the other without any actual rendering.
Highest data rate does not always yield the best picture quality. There are many variables in video compression. I've read that there is nasty macroblocking in XAVCS @ lower framerates. Seems like Sony still needs to tweak their format.