Differences between AC & DC brushless

Except for encoder type, are there really any differences between a
DC brushless motor and an AC brushless motor? (I'm talking about
servo motors here, not motors driven by a VFD or the mains.)

If I have understood things correctly, the difference is really in
the way the motor is driven -

* it's a DC brushless motor if the commutation is trapezoidal (which
require hall effect sensors or other low-resolution absolute
feedback).

* it's an AC (brushless) motor if the commutation is sinusoidal
(which require some kind of higher-resolution absolute or semi-
absolute feedback device).

If this is correct, then I wonder what is the result of using the
different drive methods? How much "better", and in what ways, is the
AC approach?

Arvid