You can be pretty much guaranteed outstanding optical quality from the Big Three (Zeiss, Leica, Swarovski) and the prices can be quite steep, but on the other hand you'll save yourself some second-guessing as to if you could have gotten better. European glasses generally use an optical cradle design to hold the lenses and prisms, while Japanese glasses usually epoxy the elements in place. Theoretically, the elements can be knocked out of alignment easier with cradles, but you can get them repaired. With expoxy, you can forget about repairs if your glasses are hit hard enough to disturb the alignment.
Other factors to consider:
Field of view - Wider is usually better.
Close focus distance - Essential if you plan to do birding.
Waterproof & fogproof - Standard for marine binoculars, fogproofing is usually achieved by purging the interior with dry nitrogen so there is no water vapor to condense inside the binoculars.
Eye relief - If you wear eyeglasses 18 mm is a general minimum, the longer the better, and twist up/down eyecups are a plus.
Spherical aberration - You have to test this in person, but look at something with straight lines near the edge of the f.o.v. If they curve too much, you've got bad spherical aberration. I had a Steiner 8x22 monocular that suffered from this. You can also look for chromatic aberration, but you'll probably need a color chart or something.
Weight - Every ounce counts when you're traveling, believe me.
Armor/lens covers - Rubber armor is pretty much standard these days, but not always. I like how Steiner lens covers stay with the glasses, as opposed to the common individual ones that are easily dropped/lost.
Porro/roof design - This refers to the prism layout. Porros are those wider, step-tubed binoculars; roof prism glasses use straight tubes. Roof prism designs are more compact, but require higher tolerances and suffer from more light loss. These can be offset by superior quality and coatings, of course.
I wanted something compact, roof prism design, 8 x <30, weatherproof, long eye relief, phase coating. Pentax 8x28 DCF MP's fit the bill perfectly, at about $200. I also considered the Brunton Eterna 8x25. Then again, I only use my binoculars for hiking and traveling, so evaluate your needs and choose accordingly.
