The Metolius Safe Tech Waldo is our current favorite big wall climbing harness. It is the most comfy harnesses we tested and is also ideal for rigging, course setting or any application where you are going to hang around a lot. This is the most popular harness among climbing gym course setters, which says something. This harness costs $129, which is more expensive than the Petzl Calidris and Black Diamond Big Gun.
Compared to the Black Diamond Big Gun this harness is more comfortable with better gear loops, but it is heavier, doesn't breathe that well, and you can't take off the leg loops. We still prefer the Waldo but there are some big pros to the Big Gun. Compared to the Calidris, the Calidris is also lighter, breathes much better, and can be also used as a free climbing harness (we wouldn't use the Waldo at the crags). However, the Calidris doesn't have the two belay loops, super bomber gear loops, and was not nearly as comfy. So we go with the Waldo and choose it as our fav big wall/rigging harness.
If you are just going to do a handful of walls and are on a tight budget, we would lean toward the Black Diamond Momentum, which won't be as comfortable but is only $45 and can be used for just about every type of climbing. We have done a lot of walls in harnesses with equal padding to the Momentum and while the hip area may get rubbed a little raw, it's not that bad as long as you are not hauling massive loads.
Since we wrote this review, Metolius has increased the price back to $130.