I've used a pump filter (MSR Sweetwater), iodine (with horrific results), Katadyn MicroPur (chlorine dioxide tablets), the Steripen Adventurer and the ULA Amigo Pro gravity filter.

The pump filter consistently threw my lower back into spasms while I was bent over the water source. The Steripen (see my recent post) has been returned to REI. Its on-off switch is so stiff that most of the time I couldn't turn it on, and I was concerned that there was no way to sterilize the water remaining on the threads or the outside of the wide-mouth jar required. The Steripen may seem like the lightest solution, but by the time you carry extra batteries and the required wide-mouth Nalgene bottle (4 oz.), it is heavier than my preferred solution. With the extra batteries and the Nalgene, it's heavier (and takes longer per gallon) than my preferred treatment method. My experience with chemicals has not been happy; the allergy to iodine resulting from my use of iodine purification 20 years ago has left me unable to tolerate seafood or anything cooked with iodized salt (meaning I can't accept most invitations, since most people use iodized salt).

My preferred water treatment is the ULA Amigo Pro gravity filter, 7.5 oz., $45 US, a gravity filter using the Katadyn Hiker Pro filter cartridge. In a situation common to most of the "cottage" gear manufacturers who work out of their basements or garages, the owner of ULA, Brian Frankle, is going on a hike starting Aug. 1, so unless you want to wait several months, you need to order by this Thursday, Aug. 24. While it's inconvenient, I can't object to these folks doing the same things I like to do--and the gear they produce will be the better for it!

YMMV--Your Mileage, obviously, May Vary!