S-Tec System 20/30 Versus System 40/50

A pilot friend insists that there is a fundamental difference in the way
these two systems operate. I am thinking about installing an autpoilot and
since I have the extra panel space, I would like to get the System 40 or 50
for (what looks like) a more user-friendly interface. However, he claims
that the newer System 20/30 is better at handling its duties in a number of
different aspects.

Can anyone point me to an article or maybe share their experiences? Google
turns up nothing.

Thanks,

Marco Leon
N36616