I guess it really depends alot on what you hope to accomplish, and what conditions you are typically hiking in.

If you are in a consisently damp area, or would find yourself on a boat, waterproof would be almost a necessity.  If you are an avid birder, high quality optics and magnification are more important.  If you are looking across the countryside, or also using them at sporting events, then a wide field of view would be important.  If you're hiking in rough terrain, where damage is a distinct possibility, you may not want an expensive pair, or would want a rubberized or armored pair. 

Personally, I keep a pair of economical, compact binocs in the hip-belt pocket of my day-pack on nearly every hike, just in case I see something interesting.  They're lightweight and unobtrusive, and perfectly adequate for those needs.

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