It's great that we have so many options in the baby carrier department these days and it seems the trick is to find the one that best suits your family and lifestyle. We're betting the Kokopax carrier, a more recent entry on the scene, will fill a niche for many people.
Frame carriers used to be more popular and we sometimes see very old ones at garage sales, but besides the Kelty carriers which we see used more for backpacking and hiking trips, there aren't many frame carriers on the market nowadays. The Kokopax is lightweight - under 3 lbs - and can be used for kids up to 35 lbs. or around two years old (starting from about 6 months). Having your child on your back seems particularly useful when you have more than one kid to wrangle as it leaves your hands free and could also free you from using an unwieldy double stroller. This also strikes us as a very dad-friendly option.
At $179 the Kokopax is more expensive than most carriers we've seen (including the popular Ergo which also allows for back carrying), but if you do a lot of walking and baby carrying it could be a wise investment. You can check out all six fabric designs and read more here.