I dislike topless because it invites wayyyy too many bugs to lay eggs into my tanks, and I don't like the evaporation rates. A plexiglass or glass lid is just as pretty to my eye and reduces a lot of the possible predators that could make their way into my tanks, thanks to the other half who loves pretending that he was raised in a barn and leaves the doors open.
Mine are all topless right now; heavy layers of floaters seem to be discouraging jumping. But the evaporation is making me crazy--that's a lot of distilled water to lug. I'm thinking of going to clear glass tops.