"I've got a Panasonic HC-V750 camcorder which supports AVCHD and MP4.
The highest quality AVCHD settings are called "1080/60p", while the highest quality MP4 settings are called "1080/50M" (also at 60p).
Both are 1920x1080 full HD resolution.
When I check out some sample files recorded in those 2 formats with MediaInfo, I see the AVCHD bitrate is variable and seems to be in the 22.8 - 25.0 mbps range, while the MP4 bitrate is close to the advertised "50M" at a variable 45.4 - 49.2 mbps.
So, although I know the answer is a bit subjective, I am interested in which format people think has better video quality. By bitrate and file size alone, I would be inclined to say MP4 in this scenario. But the instruction manual implies that the AVCHD is better quality.
FYI: on the audio side, the AVCHD has AC3 384 kbps 6 channel audio, while the MP4 has AAC 128 kbps 2 channel, so the AVCHD AC3 audio clearly seems superior."