As far as features, first off decide whether you want an external frame or internal frame pack. External frame packs are great for carrying heavy loads over relatively flat trails.  Then are generally cheaper and because the pack rides away from your body, you'll have air circulation between  the pack and your back.  Frame packs on the other hand tend to be a bit constricting so if you are on more rugged terrain you would probably be better off with an internal frame pack. Internal frame packs ride close to the body and allow for more freedom of movement. Next, do you want top loading, panel loading or both?   Do you want an internal hydration sleeve, or outside water bottle pockets, or both?  Do you want a lot of pockets to keep your gear organized, or to you prefer to cut down on weight and thus have few or no external pockets?  Do you want a lid that detaches and can be used as a lumbar pack for day hikes? Do you want ice axe loops and/or ski sleeves for winter trips?

CreakyKnees hit the nail on the head, the best pack is one that fits and has the features you want.  I can recommend a pack based on my feature preferences that you would hate and I can recommend a pack that fits me perfectly, but is uncomfortable on you.  Stick with quality brands though.  Some good ones are Deuter, Mountainsmith, Gregory, Osprey, GoLite, Marmot, Arc'teryx, Granite Gear and Black Diamond.  REI and LL Bean also sell quality packs under their brand names that are good values.   Size is another consideration.  If you're just doing weekend trips you don't need an expedition sized pack because you either aren't going to fill it and it will not ride properly, or you will tent to try to fill it and carry waaaay more than you really need to. Nor do you want to go too small and wind up hanging equipment from the outside of the pack.  For weekend trips 3,000 ci (50 liters) to about 5,500 ci (90 liters) should be sufficient.  Since a 12 year old can't be expected to carry a lot, you might be better off leaning toward the larger side.

Osprey makes good packs, no doubt. However, the best pack is one that 1) Fits (very important, the coolest pack in the world is a curse if it does not fit properly), 2) Holds everything you need/want/intend to carry, and 3) Has at least most the features you want. If you live witihin convenient driving distance of an REI or other reputable outfitter you might consider renting (or borrowing, if possible.) If you are like most people, you will likely go through several packs before you settle on "THE" pack, and you will likely end up with at least several (one smaller-load/day/short-trip/etc pack, and one for more serious outtings.) For myself and being somewhat old school (and carrying more than is currently in vogue), I'd have a hard time fitting all my stuff into 44 liters. I get a lot of looks and comments, more so because of my age (55) and because I'm usually carrying it all myself, but on the other hand every time I've gone out in the last two years (since getting back into this) I've ended up helping other folks out (food, drink, repair kit bits and pieces and tools, stuff out of my first air kit.) If you're new to backpacking you might want to try to get inolved with some clubs or the scouts (or church etc groups) with your kid, or perhaps some Meetup groups and get some experience and a brain dump. At a minimum be sure you know (and take) the ten essentials, that you can apply them (especially the stay warm/dry stuff and the navigational parts), etc. Good luck.

Osprey Talon 44 Pack it would be a good pack of it has good guarantee for a pack and it sits well and a This year Osprey celebrates 35 years of independent innovation. Our constant dedication to superior quality, design and craftsmanship backed up by a solid warranty has gained us countless loyal customers and an exemplary reputation for producing gear that truly lasts a lifetime. Therefore, we thought it only appropriate to celebrate our 35^th anniversary by launching an all encompassing guarantee – any product, any reason, any era – The Osprey All Mighty Guarantee.