I prefer ammo cans too, but they are expensive, big and difficult to hide in urban areas, and they get stolen - a lot. I've lost a couple myself....
The Ottawa Bomb Squad has also mentioned that they are difficult to assess with their fluoroscopes so they're likely to get 'disrupted' if deemed a 'suspicious container'....

The brand name Lock'n Lock containers are fairly durable, (the knockoffs have all the faults that kahja noted), come in a variety of sizes and, because they are clear and the contents visible, rarely cause bomb scares. In urban area's they remain the container of choice, but in the deep woods an ammo can is indestructible! It's very disappointing to hike through the woodlands of Deep River last weekend and find a great little trail littered with micro-caches! There was only one small cache on the trail - "Where are the Cranberries"
http://coord.info/GC235PW , but that's a different rant altogether!

Any container will suffer with the weather and the clumsy cachers who force them open or dig them out of the snow, the cache owner must maintain them as required. But no geocache needs to be mistaken as a bomb by the general public, or destroyed by the Police, if the container is chosen wisely for the location it's in.
Blue -