It can also depend on where you live and the time of year.
If the sun is only out for 8 hours a day then it is likely to be quite weak sunlight.
But where I live in the sub tropics the winter sun is about 9 1/2 hours but it will
still give you sunburn, so in my case I would prefer the sun.
If I lived in the UK or Canada I'd go for the HID's.