Depends on the species. I've seen panthers and Veileds do amazing under powersun bulbs, especially for 36" or taller cages. A lot of my customers have a much easier time raising their baby chams (again, primarily veileds and panthers) under the mercury vapor bulb, as it's a nice hot light with lots of UVB, making it perfect for species that like to bask like those do. Montane species or more delicate species are better off with a fluorescent tube like the reptisun, which allows you to control the basking spot wattage etc much better.
-Jen