I cover my 36 bowfront with saran wrap because I was foolish and bought a T5 that doesn't allow for a lid. With my tank running at 79-80 F and my room getting down into the low 60's at night, I get a large amount of condensation running down the wrap and it doesn't dry up till about midday. My airflow comes from behind and the sides under the light where I've left it open.
I plan to use a lid on my 40b (not setup yet). I'll use it partially to block a slight amount of par and also to prevent evap. I'll likely leave the front flap raised for air flow. I've seen my filter outflow move the water in a way that wafts around my saran wrap cover...., I figure the front flap will do well enough to allow air exchange.
Lastly, I'm not embarrassed to say.. I have a big problem with dust. I already deal with the biofilm on top, but the dust just makes it so much worse. The entire central air system in this house needs to be cleaned out.
I really like the look of open top, but when I try it, I end up having to clean the topwater and top off the tank very often. I don't own a python yet and I really hate my buckets.