the Kelty we tried was HEAVY and difficult to adjust. returned it.

REI Piggyback is a solid carrier. i hate the belt on it but my husband likes it a lot. he's put in a lot of miles with the Piggyback.

my favorite is the Madden Caravan, which is now the Sherpani Rumba. reasonably light, tons of capacity. the thing i don't like about it vs. the Piggyback is that the Caravan doesn't have space for a hydration bladder against my back. i hope the Rumba has fixed this problem.

i've never used one, but have heard raves about the Deuter Kidcomfort carriers.