I have a glass top on one side and I have eggcrate on the other. I get slightly less evaporation (I assume) but still get the air exchange. If you got topless, I would at least get eggcrate. You still could have a fish jump if startled or something could accidentally fall in.
Topless all the way. Less heat so its easier on my chiller. Easier access. And if your running MH u get that cool shimmer effect! I've only had a few jumpers over the years but at the same time they were known to be jumpers. But there is always that risk. I say if they want to get out that bad then let them go. Lol
Don't bother with a glass cover. Either go open top or canopy. They both have advantages and disadvantages...
A well made canopy (with proper fan circulation design) will not have more heating problems. You will end up evaporating a bit more water with the air circulating over the water due to fans though.
I choose canopy for two reasons: No carpet surfing fish and lack of light spill over into the room. Glitter effects will happen in either open top or canopy if you are running MHs.