I have a D8, and like its sturdy construction and versatility. The dual bulbs provide some assurance that you'll have light when you need it. Also, the lantern grip can be inserted on either side of the light (putting the switch on the top or bottom of the light), and for more options, you can get a pistol grip, if that is your preference.
The hot spot on my light, although not round, is very smooth. The surrounding beam is somewhat splotchy, but for practical purposes, and depending on your use, it probably doesn't matter.
I use my light strictly on land, but if you're going to use it underwater and want bright, perhaps the D8R is the way to go. If my understanding is correct, this rechargeable model comes with one 14-watt bulb, and one 30-watt bulb (underwater use only). Printed burn times on the D8 are 7-10 hours, and on the D8R, 1.5-3.5 hours.