I'm using the ULA h20 Amigo, albeit modified depending on my needs. I replaced the stock drawcord water bag with an ultralight 4 liter waterproof drysack. This way, I can hang the bag in camp and have extra water, and also wash my hands without fear of spilling any water. The stock drawcord bag, which doesn't seal close at the the top, would sometimes shift postion and leak or spill water out.
I also can use a General Ecology First Need replacement canister instead of the stock inline filter. The GE canister, as per the manufacture's specs, can be used in gravity filter mode sans pump. This canister is the only mechanical "purifier", not filter, that is EPA rated to remove viruses, protozoa, and bacteria without the use of iodine or other chemicals.
The canister is slighty heavier than the ULA supplied one, but I feel a little bit safer that no matter what water I might encounter, it will be 100% potable.