Depends on whether you want a backpack portable or non-portable. Berky’s are about the best you can get for non-portable http://www.berkeywater.com/start.main.html
Looking at their web page, it appears many of their products, like the Big Berkey, are not available in California. Any idea why these products are not allowed in this miserable state?
We use a Doulton stand-alone, two-element, gravity unit with ceramic filters. Doultons were invented during the reign of Queen Elizabeth I during a cholera epidemic. You can pour just about any nasty water through it, and it comes out drinkable. The activated charcoal supposedly lasts 6 months, but the filters themselves are scrubbable and almost infinitely reusable. In six or seven years, we have only changed filters once, and I can’t tell any difference in water quality or flavor since new. I think we paid about $200 or a little less.