In practical terms, I ran an experiment: I burned seven segments of a quite large movie, 1 hour 18 minutes 1920 X 1080, Dolby 5.1 audio, in Pinnacle 17.6; each segment was produced as an M2TS file.
I then loaded the seven segments into Premiere Elements 11, and burned a Blu-ray - it came out at 12.2 Gb, an m2t file, and was of indifferent quality with 'tinny' sound.
I loaded the SAME seven segments into Pinnacle 17.6 and burned essentially the same Blu-ray (except for Adobe menus) - it came out at 23 Gb, m2ts and was a vastly superior visual and audio product.
On a technical basis I wouldn't know, but in practical terms m2ts is far higher quality with a consequent increase in file size.
So for me, m2ts is far better