I've told this before on other threads asking the same question and I will again here:

On a cloudy, misting, 50 degree day at the Cabela's in Grand Forks N.D. I took a Nikon, Bushnell, and Leica (all 800 +/- models) outside of the store at the same time. (VERY IMPORTANT! DO NOT BUY ONE BASED ON HOW IT PERFORMED IN THE STORE. IF THEY WON'T LET YOU TAKE IT OUTSIDE, BUY SOMEPLACE ELSE)
On a TV sized rock at the end of the parking lot (57 yards if I remember right) all of them performed very well, but already the optics of the Leica were much brighter. At a tree about 150 yds it was hard to see the little aiming dot on the bushnell in the overcast weather. At a car grille parked across the river (about 375yds) the Leica was the only one that I could see clearly and get a consistant reading on. The optics of the others compared to the Leica were like putting on sunglasses on a cloudy day. I chose the Leica, that was three years ago and I have been very happy with my rangefinder.