The Katadyn pocket has a well-deserved reputation for reliability and durability. It is one of the pricier filters but is also rated to pump much more water than its competitors. The Katadyn pocket isn't light (20 oz), but the better competitor pumps are also about 16 oz., so this isn't too much heavier. Some of the others pump a little faster, but they are usually 0.3 micron filters, whereas this is a better 0.2 micron filter. The Katydin pocket is also the only pump with a lifetime warranty (excluding wear of the ceramic filter). If you search the web, you'll find a lot of reports of the $75 pumps eventually breaking, so if you have to replace them (or their short-lived filters), you've already spent what it takes to buy this. This thing is pretty damn tough, and the only way to break it would be to take it apart and drop the inner ceramic filter.

I've found it easy to use, though you need to hold it upright to keep water flowing. During trips through the Sierra Nevada, Utah and Wyoming this filter has never disappointed. Tips to extend the lifetime of these/reduce the need to clean:

1) Use running water from streams/rivers whenever possible
2) Position the floater so that water intake comes from the top of the stream and not the bottom (where a lot of sediment stirs about)
3) Rubber band a coffee filter around the prefilter to keep large particles out.
4) After pumping, unscrew the filter and drain the excess water. The filter is silver-impregnated though, to prevent microbial growth.

If you want to keep your packing weight down, carry your water in collapsible water bladders instead of thick plastic bottles. You can buy a cheap adapter so that water is pumped from the filter right into the water bladder. If you search around the web you can find the Katydin Pocket for around 180 or less. I tend to pack light and have lots of fancy lightweight gear, but I am serious about my water sources and don't plan to compromise on this beauty.
5 stars

My husband and I love this filter, it is absolutely hard core. Not only awesome for the backcountry, but also in cases of community emergencies. You will need no other. 5 stars

I have one of the originals from the early 80's that has seen many parts of the world and has always worked for me.
Used extensively I have replaced the element several times.
Cost means nothing compared to having the runs or worse.
5 stars

I have to admit I haven't even used this water filter. My wife and I bought it in case of an emergency. I did an extensive amount of research and settled on this filter, as it seemed to be the most reliable and capable of filtering the most water, hands down. When we received the filter, we were both amazed at the quality. This is no Chinese product. It's extremely solid and feels like it will last for years to come. I was very pleased with my purchase. 5 stars

I've used a number of different filters now. It's really a matter of what you want to spend your money on. This one is spendy but the quality is great and it's size can't be beat if you're constrained. I'd give it 5 stars if it was just a little cheaper. 4 stars