I don't know if it's the best, but I'm really happy with my Osprey Kestrel 48.
I've used it for a couple of overnights, and it's tight but fits everything I need. Last night's load included a ground pad, sleeping bag, tent, a heavy fleece, extra blanket, pillow, saw, first aid kit, tarp, two litres of water, food for three people, and various odds and ends. It was a little tight, but I had no issues fitting everything.
If I cut down a bit, I think I could carry enough food for myself for a couple of days in addition to all that.
It's also very comfortable. There's plenty of padding without being bulky. The bit that's against your back is pretty well designed to increase air flow. It's easy to fit snugly so that it doesn't slide around.
Good points:
Lots of little compartments. Two pockets on the outside of the top, one on the inside. Two side pockets that run the height of the whole thing and are much roomier than they appear. The belt has two pouches, each the size of a fist. Lots of points to attach stuff on the outside. Comfortable as all get out. Attached, removable rain cover. Two pockets that each easily fit a 1L water bottle, plus an elastic mesh pocket that's large enough for a third litre or a long sleeve shirt. Hydration bladder compatible (large enough for 3L bladder).
Bad points:
The top cover is too snug, and sewn to the main body rather than attached by adjustable straps. This makes it a little awkward to get it closed, especially if the pack is full. The spot for the hydration bladder is pretty tight, and you'd need to put the bladder inside before packing the main body of the pack. The bottom cinch straps overlap the side water pockets, so you've got to cinch it after your bottles are in, then removing them loosens up the straps.
Overall:
The goods far outweigh the bads. I really love my pack, and I'm very glad that I bought the thing.
Best uses:
It's just too big for a short hike; you'd never fill that much room. It's very roomy for a day hike, with plenty of space for water, food, picnic gear, etc. It's just perfect for an overnight, unless you're a gear horse. If you pack light and well, you could do a weekend. Unless you have good foraging skills or are near enough to civilization to go back and resupply, I wouldn't go longer than a weekend without a bigger pack.
I have read reviews of the same pack, and climbers seem to love the thing for day hikes followed by climbing. I cannot comment on this first hand, but I thought I would mention it.
