Like him, I thought the sawzall would be the best (and it might still be for vertical pipe, I dunno)
But either way, all of the ways to cut pipe seem to take about a minute more or less.
YMMV, closed course with a professional driver, no Flock cameras were harmed in the making of this video, obey all local laws, etc, etc, etc
The difference between Sawzall and circular saw is a carbide tipped blade. BTW the circular saw is the loudest thing on the planet when cutting metal.