I never had any luck with the First Need filters (I've owned two of them). They always seemed to clog quickly, even with relatively clean backcountry water sources.

On the other hand, the Katydyn products (formerly PUR), have been amazingly reliable and have handled tremendous filtering loads and abuse without any problems for me.

I will put my trust in a Katydyn filter with chlorine and iodine as backups. For particularly turbid water sources, a large staging container should be used to allow for both settling of heavier contaminants and floating of hydrocarbons (like a septic system).

Cody Lundin's books do a good job of describing several other options (natural UV, distillation, etc.)