Water treatment methods:
1) No treatment. Studies have shown in most backcountry areas of the Western US this is pretty safe, and people are far more likely to bring a pathogen into the backcountry than get infected with a pathogen from the backcountry. I don't like this method for peace-of-mind reasons.
2) Classic pump filter. I have had several Katadyns. They don't work on viruses, and there is some debate whether they do much on other pathogens. They are heavier, and will break with use. They are better for filtering larger amounts of water than some other methods, but pumping sucks.
3) "Flow" filters (Sawyer, etc.). I have these too, and like that they are at least as effective as a traditional filter and easier to use. I really like the inline filters because you can just dip your bladder and drink as you go. Downsides are similar to regular filters, but the biggest drawback is they WILL freeze in the cold and break, so cold weather use is limited.
4) Drops/tablets. They are ultralight and convenient. I don't like the wait times or the taste of some methods.
5) UV Treatment. I have a steripen and this is my favorite method for areas with a lot of water, because I can save weight by only taking a quart at a time, and filling as I go. It is quick and easy. It deactivates everything, including viruses. You do need pretty clear water and you depend on batteries. Works in the cold.
6) Boiling. By far the safest method. It is slow, and you end up with really hot water. It takes fuel to do it.