I use the Hiker filter from Katadyn. For me, it has the right mix of ease of use, water flow rate, weight, cost, and quality of taste. I've also used a First Need (didn't like the way you had to hold it to pump), an old timberline (no longer in business and the filter had a tendency to fall off the hose), and a pur hiker (no longer made- the Hiker is sort of the replacement). If you have a big REI near you, you can try them out in store to see how hard they are to pump and how long you have to pump to fill you water container(s).