The Black Diamond Big Gun is a tricked-out big wall climbing harness with lots of extras: extra belay loop, extra gear loop, and multiple options for clipping gear to the back. It is supportive and comfortable without being too big or heavy.
We found it a little more comfortable than the Petzl Calidris but we like the speed adjust buckles and ventilation on the Calidris. The advantage to the Calidris is it is more streamlined and more suitable for cragging. The Big Gun is just a little too cluttered for cragging. Compared to the Metolius Safe Tech Waldo, the Big Gun is as comfortable and the gear loops are not nearly as strong or easy to use. But it is also much lighter, $10 less expensive, ventilates better, and is easier to adjust and free climb in. Overall, if you want a serious big wall harness or rigging harness, we prefer the Waldo because of its comfort and bomber gear loops. It's hard to say what we would prefer between this and the Calidris. The Calidris is better suited for free climbing, easier to adjust, and vents better. But it is not as comfortable and does not have two belay loops. Tough call.
Only occasionally hopping on big walls and running off a smaller budget? Then consider the $45 Black Diamond Momentum. It's not as comfortable, but it is manageable and up to just about any kind of climbing. It might rub your hips a bit raw, but it's not so bad for infrequent trips up walls. Beware that if you're hauling monster loads, though, the Momentum is not a good choice.