There probably isn't a single "best" bulb and wattage. It all depends on your camera, the size of your "studio" and how your lights are set up.
The camera that I use is a Logitech c920.
I currently use 14 watt CFL bulbs (60 watt incandescent equivalent).My studio is about two feet square. For the most part I use two desk lamps, but I have three if another is needed. I have tried 23 watt bulbs, but because the lamps were so close to the set they produced a lot of glare. So it would make sense that the further away your light source is from your set, and the bigger your set is, the more wattage and lights you would need.
I have found that the Daylight bulbs produce the best image brightness and color wise.
I use good old fashioned paper to diffuse the light.
With a little trial and error you'll find what works for you.
Hope this helps.