I prefer the incandescent hood b/c 1. they are cheaper, and 2 there is a variety of bulbs you can put in them including florescent bulbs So what is your preference.
(i prefer florescent bulbs for my incandescent hood )
Florescent. Like he ^ said, they can be cheaper, they're much cooler on the fish (so they dont give out very much, in fact very little heat)
I also think it look better on the tank. It takes color brighter.. much better....
Besides all the reasons everyone else has listed for Fluorescent, it helps my plants grow better. And almost every tank I have has live plants. Not to mention the fact they came with a lot of my tanks, so I didn't have to buy a hood!
I have always used flourescent. We recently got a tank with incandescent, and we immediately modified it to hold flourescent because the colour looked so dull and yellow. Plus, my plants love it.