I debated answering this, but the only real difference in ADSM on those
systems is in our IO.  Currently on MVS our disk IO for the database and
the storage pools is more efficient.  Not a lot, but it is better than the
IO path we use on VM.  Tape IO bandwidth seems to be the same.  You may have
different tape library management on VM than MVS which could sway one
position over the other.

I personally can hardly logon to MVS, but have done many things on VM, so I
run a server on VM because it takes much less work for me to do so.  Others
are just the opposite.

Bottom line is there is no good answer here.  It depends on your
sites' use of the systems.  If you have both then choose the one that
is easier to setup, configure, and run.  The ADSM commitment is equal
on both the systems.  ADSM is an application on the system, thus the
probability of a software bug bring down various other subsystems is
very remote.

Aggregate throughput (multiple workstations running simultaneous to
the server) going to disk will be faster on MVS than on VM (DB
updates and storage pool updates are all disk).  If you go to tape
they will be basically equal.  When operating in a realistic
day-to-day environment the ADSM activities are erratic, thus you do not
notice the performance difference.  You only notice it under closely
measured conditions.

Its more of a religious argument than a technical one, thus choose the one
that feels best to you and your installation.

Paul