..Did you try it in twilight situations? . . .I'm going to try the 15X50 and 10X42 tomorrow. And also the Nikon 14x40 VR. Damn I said I want to keep it under $500! Look what you all have done to me.
No, I didn't try them in twilight; our excursions on zodiaks were all in daylight hours (you don't really want to be wandering around polar bear country at twilight...), so that might very well be a major consideration for you.
I guess it's just like camera lenses -- if size, weight and cost aren't an issue, you ALWAYS want more light-gathering capability! Hell, I use these Oberwerk binoculars (on a tripod) at my weekend place to be able to count feathers on eagles and other birds that tend to land on some nearby pilings, but they're obviously not for carrying around! 
You've got to decide how you want to balance the relative importance/trade-offs of:
- Magnification (looks like you're looking at 10-15X)
- Light gathering ability, i.e., "bigger glass is generally better" (the three you're most interested in are 40-50mm)
- Size and weight (most directly related to light-gathering ability)
- Image Stabilization
- Cost
I tried the Nikon VR's and just didn't like them as well as the Canon IS...personal preference I guess. I also figured my wife would be using the binoc's more than I would, since I typically have my eye behind a camera viewfinder instead
so size/weight was a definite consideration.
I'll trade a slight loss of light-gathering in the 12X36 to get the 12 vs 10X magnification, and I'll trade IS for the advantage of both magnification AND light in the 15X50. Bottom line: do just what you're planning to, which is TRY THEM OUT and see what seems most important to YOU. All of the ones you're looking at look like excellent binoc's to me, so I'm sure you'll be happy whichever way you go! Good luck!