I never considered a filter until sitting at Moose Pond L/T in the Adirondacks one steaming August day in '91 with my bandanna and iodine tablets. I waded through the rushes into stagnant smelly water - It was the best I could find. I strained it through my Bandanna folded 3 times and used tablets. That water stunk horribly, but I was thirsty. After that my first stop on the way home to Buffalo was at EMS for a filter.
I used a First Need from around '91-95, a Pur Scout from 95-99 and an MSR Miniworks since. I beleive the First Need is still classified as a purifier. The difference being a filter removes particles down to a certain size, while a purifier would do the same but also kill any viruses. I have read numerous times that there isn't really a need for a purifier unless traveling to 3rd World countries.
I wasn't too crazy about the First Need as it is bulky had ridiculously short hoses and if I recall, had a single action pump. Having dropped it once, I can attest that the inside filter element can break. I think the FN use to come with a small bottle of dye (or did I use plain food coloring) to tint some water to test the filter for damage.
I didn't like that the filter was not field maintainable, which may not be an issue for weekend trips.
The PUR Scout was an excellent filter with a double action pump. Quck and reliable. I was always curious about the iodine resin matrix filter and how it works so quickly (...and as we all later found out...). I didn't like the iodine matrix, but I did like the charcoal filter, which was supposed to help the taste. I would probably still have this filter if PUR hadn't changed the filter element from one that could be cleaned, to the fluted paper element.
I did have one problem with the PUR and backpressure on day 2 of an an 8-day trip in '97. My buddy, Andy, and I worked feverishly on it for 2 hours learning everything there was to know about the PUR, while sitting on some rotted logs by a stream. We discovered that several almost microscopic grains of sand had lodged against an 0-ring, embedded in the silicon lubricant, causing the pressure to build up on the backstroke. Once it ws cleaned, we were fine.
I then bought the MSR Miniworks and it has run like a champ ever since. I have had absolutely no problems, it is forthright and easy to clean (and I am still on the first filter element). I like that the housing is transparent so I can see the water flow.
FWIW, I always use a coffee filter wrapped around the end of the intake nozzle and held in place with a rubber band - even if there is already a pre-filter. I find it does preserve the life of a filter and cuts down on cleaning (you can usually judge if the filter element needs cleaining by how difficult it is to pump and how many strokes it takes to fill a Nalgene (60-80). I replace the coffee filter about once every other day.
When judging filter life and number of gallons, be cautious and realistic. A filter that is supposed to last 250 gallons will do so with reasonably clear, clean water. Murky water, vegetation, sand, mud and microscopic creatures (like in pond) will drastically cut the life of a filter.
On longer trips I usually carry a backup of Tincture of Iodine. I store it in a dark glass eyedropper bottle (pharmacies will sell you a dark eyedropper bottle for $.50 ~$1.00). I used this as my sole source of water purifying in Alaska in 2003 because I was worried about all the silt in the glacial runoff clogging a filter. Tincture of Iodine is cheap and while it doesn't taste that good, it is easy to have on board - I usually add 5-6 drops per liter of water.
I hope this helps. I can't tell you anything about the funky new Mioxx or the UV purifiers - They are out of my element