Also take a look at the First Need XL from General Ecology. A bit larger and heavier than the Katadyn Mini, it is also faster (1L/m) and more effective (0.1u). Several of the people I backpack with have this unit and it's very versatile and reliable. You can maintain it in the field by backflushing with clean water, and you can set it up as a gravity-feed filter for hands-free filtering.

I have an 18 year old Katadyn (was PUR back then) Hiker Pro that still works fine. All I've done is replace the cartridge a few times and perform the required maintenance after each trip. It came with an Iodine cartridge to kill viruses (which are too small for any filter), but I never used the Iodine cartridge in the field (tried it at home and didn't like the taste).

The MSR Sweetwater is another unit to look at. Smaller than the First Need, more effective than the Hiker Pro or Mini. This would be my second choice if buying a new filter.

Finally, I also have what I call my Frankenstein Filter for day trips:

• Sawyer Point Two water bottle filter cartridge
• Camelback Bite-Flip top from their .75L Better Bottle
• Standard 1-Liter Nalgene Wide Mouth Bottle

The Sawyer filter cartridge is rated at 0.2u, which is good enough for Crypto, Giardia, Salmonella and most forms of E.Coli. It does get a bit tough to suck water through the filter by the end of the day if I'm using dirtier sources, but I just backflush it well when I get home and it's good as new for the next trip.