I tried many of my friends' backpack carriers before finding the Tough Traveler. They were all cute but not comfortable. So I got online and started searching backpacking, hiking, and outdoor sport newsgroups. Everybody was raving about the Tough Traveler Kid Carrier.
The best part of this pack is the fit. Some people may complain that there are too many things to adjust, but I love the custom fit it provides. My husband and I were both able to make it fit us perfectly, even though he has a long torso and I'm all legs. The load is well distributed by the shoulder straps, chest strap (be sure to use it, it makes a difference), and waist belt. My back doesn't get all sweaty with it, like with other packs I tried. Our son loved riding in it. The sides supported his head well if he nodded off. Our son is almost 4, and my husband can still use it. I'm just not strong enough!
The cargo bag has enough room to store stuff for a day hike, and you can strap other bags onto the frame if needed. Also, it has two loops you can attach toys or a water bottle to, within reach of your child.
You have to learn how to put it on. Example: Open the stand, place the child in the pack and strap child in. With pack slightly to one side of you (let's say the left), grab the handle loop (on the top) with your right hand, and lift and slide the pack up the left leg. Put your left arm through the shoulder strap. Shrug your shoulders to scoot the pack to the center of your back, then slip your right arm through the right strap and buckle yourself in. Easier than it sounds, once you do it a couple times.