I think there’s actual logic here. If you’re storing a liquid, you’re probably going to be getting it out with a big spoon, so the round sides make that easier than flat sides and corners. If you’re storing something like lasagna, you’re probably cutting servings into squares/rectangles, so the flat sides make more sense.
If you’re storing a lot of liquid you’ll probably want to pour it out later. In that case square is better as the corners will provide a bit of spout action.
I think there’s actual logic here. If you’re storing a liquid, you’re probably going to be getting it out with a big spoon, so the round sides make that easier than flat sides and corners. If you’re storing something like lasagna, you’re probably cutting servings into squares/rectangles, so the flat sides make more sense.
If you’re storing a lot of liquid you’ll probably want to pour it out later. In that case square is better as the corners will provide a bit of spout action.