Michael, I've tried both rings on in person. As far as setting, HW has the double prongs, which looks gorgeous from the top down, and it looks really clean - they pride themselves on having least metal showing. From the side view, then I'd have to say that Tiffany looks better.
As for the stone, HW has the better stones...it is definitely sparkles more, and I'm talking about even when covered. I was trying hard to find a place where the HW stone didn't sparkle, I even held it under the table...I couldn't make it NOT sparkle. (Their pictures usually don't look as good as the real thing).
As for comfort, the HW band was more comfortable compared to the Tiffany knife edge band.
I prefer the HW over the Tiffanys one.
But on the practical side, it's a lot easier to deal with a Tiffanys ring because anytime you have a problem, or you just want a cleaning, there's always a Tiffany store around. It's harder to find a HW store.