The best choice may depend on what kind of water sources you expect to encounter. I used an MSR ceramic filter for years. They're kind of bulky, slow and tiring to use. But, they're also reliable and are supposed to be able to handle chemicals, pesticides, etc. After a pack rafting trip in Utah a few years ago, though, I got sold on the Platypus gravity filter. We didn't want to use them on the creek we floated (and dragged) our rafts down since the water had mine tailings, pesticides, and other nasty bits. But, when we were about out of water and this beautiful little oasis was the only source to be found, the gravity filters did an impressive job. In half an hour, with two filters we filled all of our carrying capacity for 10 people. And, as far as I know, there were no bad after effects.