From Patrick in New York:
If you watch in the field, you will be amazed to see how many top birders and other folks who know binoculars well carry a 7x42 binocular. The assumption by folks is often that more magnification is better but that is clearly not always the case and many experienced field birders know it. Hold up two binoculars, a 7x42 and a 10x42 in front of you and look into the eyepiece lenses and compare the size of the light circle you see on the eyepieces lenses on both pairs.
You will immediately notice how much larger the light circle is on the 7x42 bins. Having a larger light circle has the effect (one that many people don't understand) of minimizing hand shake because your eye does not fall outside of the light circle even if your hand is shaking. This results in a brighter, more color apparent, steadier view and is easier to maintain for longer periods of watching that distant hawk or looking in that leafy tree for that stealthy warbler. Also, having a bin with a lower mag makes dawn and dusk birding brighter and more comfortable as well.
The tradeoff used to be the weight because you also want the larger objective of the 7x42. With the new Ultravid HD and the new housing materials, that problem is gone. This is a bin that fits the hand very comfortably and feels like it has the same weight as the older 32 objective bins.
I did a comparison and definitely preferred the Leica HD over the Swarovski or Zeiss models in the same class (with the 42 objective) but this is a personal preference and mileage may vary. I think the Leica view is a bit more edge to edge clear with a more 3d like view. I also like the way it focuses and adjusts better than the others.
To me, a combination of the Leica HD 7x42's with the killer Swarovski 8 or 10X32 EL's (the Swarovski EL's with the 32 objective is an amazing field bin) as a second pair is a match made in heaven. For an entire day in the field, wear the Leica's in the morning and again in the later afternoon and use the EL's in the mid part of the day. Throw in the Leica 10x25 Ultravid's for a travel pair and you are so good to go. That's what I did.