yeah, I would apply the same logic as sun blockers.
in the south, the sun tend to be higher, so we use horizontal protection. Therefore, an horizontal window would get less sunlight through it, through the year. maybe not a lot, in winter it wouldn’t make a difference, and it also depends on the thickness of the wall (a 150mm wall won’t make a diff, a 600mm one will)
East west, we use vertical protection. on instinct, I would say that a vertical window would get a bit less light then.
In both cases, the thickness of the wall (assuming the window is mounted on the inside) acts like a sun protection, both horizontal and vertical.
a pair of quick and dirty tests :
late august, midday, south, you see the shadow takes almost the whole horizontal window. but less than 50% of the vertical.
I turned east, switched to winter and the vertical now looses more.
So, without any dimension, context, thicknesses or location, it’s all very theoretical, but I would say that in the south vertical get more light, and east west it’s horizontal. Inbetween (SW and SE) you’ll get pretty much the same over the year.
Wall thickness, exact orientation, time of the year will give more contrasted results, but still.
overall, on instinct, to reduce sun exposition in summer (but not in winter), I would pick horizontal windows and thick walls. Sure, in summer, it means more sunlight, but here in marseille, we would use blinds and curtains regardless. And in winter, a sunny day would be a heating-free day.