I got a little cfl set up for one of my plants, I like to hang the majority of the light about 1-2 inches from canopy, but got some side lighting to get the lower branches as well... Hope this helps
Oh ok... Really it's preference plenty of growers do it either way, or more than one light and have them horizontal and vertical, but if you only have one light to work with Id say the general consensus is horizontal with some kind of reflector if possible.
I'd probably go horizontally and get a few 26ws for side lighting. I've got a 200w cfl that I hang vertically, but I've got a 150w hps horizontally too.