I got hooked on a Sawyer gravity-feed setup a couple years ago and it's now my favorite (having tried just about everything there is to try). It's simple, easy to use, field-servicable and perhaps best of all, I can wander off and do other things while it's working.

I use the "PointONE" system because I'm not typically worried about viruses. In a pinch (really cruddy source water) I can always toss in a ClO2 tablet, but that hasn't been an issue where I hike.

Cheers,