I've only used UT but I have studied both designs. Take my comments with a grain of salt.

Both UT and PT are supseptible to the same problem: bb shell specs. Both have the same tight tolerances for shell width and bearing alignment. The hirth joint in an UT crankest is not a concern from a strength or alignment standpoint. I'm guessing the main reason why it was replaced at the lower end was cost. From an end user standpoint, I think UT is better in every way. Ultra torque only needs one "special tool" for installation and removal. The long Allen key that can be picked up nearly anywhere. Removing the bearings requires a puller, but the average consumer doesn't need it and the park tool is only about $60.