The following criteria are significant in the selection process of binoculars:

Mechanical
Solid, Quality Feel.
Good Weight Balance. 
Correct Weight – Not too heavy for carrying with you.
Comfortable in Hands.
Solid Focussing Wheel – Must not adjust too easy or too difficult.
Comfortable Size for holding and carrying.
Shock Proof.
Water Proof/Nitrogen Filled - Waterproof binoculars are sealed and filled with a dry  
inert gas which contains no water vapour and can therefore not condense inside.
Sufficient anti-reflective coatings for maximum light transmittance.

Optical
Bright Images – Very important for Bird Watchers.
Good Contrast Images - Very important for Bird Watchers and Hunters.
Good Low-Light Performance - Larger objectives and excellent glass produce bright 
images in low-light conditions.
Efficient Focussing – Bird Watchers and Hunters do not have time to struggle with 
focussing.
Wide Field of View - For Bird Watchers and Hunters this is important in order to spot a
bird/animal swiftly.
Comfortable Eye Relief, especially for eye glass wearers.
Close Focussing Distance, especially for Bird Watchers, to view birds at close range.
Magnification – Mostly 8x or 10x for Bird- and Nature Viewers are required.