I have a Sweetwater Guardian, and I like it. It’s probably easier to pump than any other filter because of the lever it uses. I do know (from using at REI) that it pumps easier than an MSR filter with a similar lever. However, if I were buying a filter for the first time, I would consider an MSR Miniworks or Waterworks or a Katadyn Pocket Filter or Minifilter. The MSR filters attach directly to a water bottle (or my MSR Dromedary water bag), so there’s no output hose to get contaminated. The Katadyn filters seem to get the most use out of their replaceable filter elements, if their claims as to filter life are accurate. All of those filters have the requisite pore size (.2 microns, I believe) to filter out cysts, protozoa, and most bacteria. In any case, check out the monthly panel here about water filters and contaminants, or go to rei.com and find their chart that compares the abilities of various makes and models of filters, to make sure the one you buy removes the things from the water that you want it to. And remember this is only one opinion (mine) among many. You may place greater emphasis on other factors in choosing a water filter. A trick to extend the life of any water filter, which I probably read in this newsgroup, is to cover the “prefilter” at the end of the intake hose that goes into the water source with a coffee filter, to strain out the larger contaminants and keep them from clogging the filter element.
