York Soaring in Ontario, Canada just switched over to MSL for the club
operations after using AGL for so many years. It was hotly debated
with arguments on both sides.

AGL is great for basic training. We teach the circuit based on AGL:
800'-1000' at the IP to start the circuit, turn base at 400'-600' and
turn final at 300'-500'. Real quick and simple, just read it off the
altimeter with no math conversion. Minimises the mental load on a
student pilot.

Causes minor problems in operations, though:
- xc pilots work on MSL but the club ships were AGL, so moving the
dials back and forth
- pilots confusing MSL vs AGL readings
- power pilots are on MSL, people would confuse heights given over the
radio, thinking it was AGL

As a concession to those firmly entrenched with AGL, we've put printed
stick-on rings around the altimeters that has AGL markings specific
for our club. The thousands pointer indicates zero AGL when set to
field elevation.