I like a Sawyer mini. Quite versatile. I like how I can set it up with a Platypus bladder and use it as a gravity to fill another bladder or whatever you want. You can also just leave it hanging there with the cap on, and filter it as needed. A tip i picked up elsewhere on the inter-webs: I wrap up the small squeeze bladder, the syringe and the filter along with a few connectors into a 1L (or .5L maybe) Aquafina water bottle with the top cut off. Keeps everything together and you can use to to collect more easily than the squeeze bladder or the platypus bladder. Other pros: very light, can be used as to drink directly from source using straw. Can also be used as permanent or semi-permanent in-line filter between the bite valve and your hydration bladder. Cons: you cannot let it freeze; you need the syringe on longer trips to backwash the filter, which adds a bit of weight. Heavier than iodine or tabs.
As someone already pointed out, many of these suggestions are for filters and not purifiers. A purifier would also kill viruses, which a filter cannot filter out. If I'm to understand correctly, viruses aren't really an issue in most (almost all?) parts of U.S. and Canada.
I've carried tabs as a backup in case I break the mini or accidentally expose it to freezing temps for too long. Once exposed, there is no real way to tell if its ruined, so you have to bin it just to be sure. You could continue to use it for silt, but you'd still need tabs or iodine or something else, anyway.
