This is copied from another thread:
I have a Wolfpack, the smallest, simplest model they make. It's just about good enough for walks around town, but wasn't meant for hiking. I have used 4 different packs.
I'm with Kanga. The Ruffwear Approach is the best I've used so far. It is very durable. I mostly like the sturdy, well-fitted, padded harness. I have often carried my dog over fast, rock-hopping streams and lifted her up or down some big ledges, using the pack's handle. And it stays pretty level if you pack it evenly. My 60lb. Akita wears a medium. My only complaints are that the pockets are too big for my needs. I pack my old dog lightly, and the pockets hang low and puff out to the sides. They drag and scrape on everything, but tearing is not even a thought since the fabric is tough! I had some fabric "taken in" to reduce this effect.
Also, I wish it was available in red for better visibility in the woods. I got blue (as opposed to green) so my dog would not blend in to the forest.
Their Palisades pack is red, but too heavy (37 oz.), with excessive bells and whistles for my liking.
The REI website will give you weight specs for everything. I think the Approach is about 21 oz. (that's a full pound lighter). They also have 2 models under the REI brand name. I recently bought their REI "Ultra" dog pack, but haven't used it yet. It has smaller pockets with compression cords. It remains to be seen if it's as good as the Approach.
If you buy from REI, you can return it, unconditionally. Can't beat that.