It's already been said, but throwing in my two cents -- the K-pump is the way to go.
We have a big Carlson (great for pumping up a boat if you don't have an electric pump, but bulky and awkward on the river, and it takes 2 people), and we have the little cheapies, and a K-pump.
K-pump has it hands down. Lightweight, no nozzle to hold in place, and decent volume. I do the Grand Canyon (almost) every year. I would never take anything different. The only thing I don't like is that it's harder to do on the fly, but for all the other positives I can overlook this one