Most birders find 7X or 8X magnification preferable, as they are less burdensome, have better light gathering characteristics, and are generally good for wide-angle viewing. 

Fully-coated optics will give a brighter image than partial. This is an important feature as birds are not always to be seen in perfect lighting conditions. 

The quality of optical glass can vary greatly. Buy the highest quality you can afford for the best clarity and sharpness. 

For the close quarters viewing of birds in a backyard is best served with binoculars capable of focusing at a shorter distance. Look for this feature if you are watching birds in your garden. 

If you wear eyeglasses it is important to fine binoculars that give longer eye relief. Leave your glasses on and use binoculars with 12-15 mm of eye relief for greatest comfort.