Hi,
As an owner of a 42 All-Glass hex tank I might be able to answer this one. Generally, as this is a compact tank you would want fish that don't require a lot of swimming room. Fish that lurk are probably the best. I made the mistake once of getting a carpenter's fairy wrasse and his constant swimming habits (with the mad dashes they are known for) were just too annoying for me.
My wrasse bass and candy bass are classic lurkers. ...
The possum wrasse is a little more active but still slow (especially for a wrasse).
I'm thinking that maybe bangai cardinals would be a good idea as they would be more visible constantly. My tank looks empty at times because of my fish's reclusiveness.
So yeah, basslets, psuedochromis (pick the gentle ones!),...a very few types of wrasses, possibly gobies...etc.:happyfish