There are almost as many choices of water filters as there are people to use them... so I exaggerate a bit but my point is there are lots of choices... and with so many choices, which is the right choice? Well, the answer about the 'right' choice isn't quite that simple but I'll try to offer some clarification and observations from personal experience. Specifically, I have 3 filters to discuss: The MSR Miniworks EX, The Sawyer 3-way, and the Steripen Classic Water Purifier. I have varying experiences with each of these. I'll discuss them in reverse order.
The Steripen Classic was my first purchase into the world of water filters/purification. I looked at the old handle pump filters as 'old stuff' and the UV light was the way to safe clean water for the 21st century. Hindsight being 20/20, I probably wouldn't buy it again if I had it to do all over, but since I have it I'll keep it. One of the things that attracted me to the Steripen was the UV light killed the common stuff we buy filters for (giardia and cryptosporidium) AND ALSO viruses. Very few filters actually stopped the viruses so I was initially excited. However, I soon learned the difference between water purification and water filtering. The problem I discovered is that the water is still silty/dirty and still has the taste of whatever water source I am drawing from. Discolored water not only turns me away, but also reduces the effectiveness of the UV lighting. Finally, as some other reviewers observed, I have also found the Steripen semi-finicky. Sometimes I'll push the button- following the same procedure as always- and the red light blinks indicating it is confused and won't work. To make it work, I have to remove the batteries and reset it entirely. Once, I actually had to repeat this process as many as 3~4 times before it finally worked. REALLY frustrating! The best use I had for the steripen was right in the wheelhouse of this product... I took it to Russia during our adoption trips and used it to sanitize tap water for brushing teeth and even drinking. Otherwise, I've since learned that viruses are not a real problem for most North American water supplies. Consequently, I'm unlikely to use the steripen on most camping trips.
The second product I want to discuss is the Sawyer 3-way filter. Reading the reviews I was really excited. I bought it online and ended up returning it before I even used it- so I can't give the product a thorough review. Why did I decide to return it without even trying it? Primarily it was the size. The product is about the size of my closed fist. While smaller than the pump filters, I expected something smaller. Secondly, I didn't think all the way through. The 3-way filter is designed to be connected to a water bladder (like a Platypus). Although I have a Platypus ziptop bag, I don't want to contaminate it with dirty water. This then causes me to carry TWO water bags (one for my dirty water and one for my clean water). At this point, almost any size/weight advantage I previously had is now gone. Finally, for many of my shorter trips, I prefer to carry my water in my REI Nalgene bottles instead of loading up the Platypus. The Sawyer 3-way made it rather awkward for me to fill the nalgene water bottles without balancing things.
The MSR Miniworks EX has turned out to be my 'go to' water filter. This ceramic filter with carbon core has performed beautifully. During my initial use, I filtered water from Martin Creek Lake while primitive camping on the island. The water came out crystal clear, tasteless and odorless. In fact, I'd even go so far as to say the water from the MSR came out cleaner and with less taste that the tap water from my municipal water supply. I also like the fact that it attaches easily to my nalgene water bottles and is field serviceable if I need to clean it. The disadvantages I've discovered with the MSR Miniworks are: 1) It takes a deeper water source to work. You need enough water to submerge the filter tip. This means I am going to have problems if/when I try to filter a spring coming out the side of a hill; and 2) Because it is a pump filter, you have to remain at the water source to filter the water. By comparison (and to give credit where credit is due), I could have used the Sawyer 3-way to direct my hillside spring into my dirty water bag and then let gravity filtering do its thing while I do other stuff.
So what is my conclusion? Well I'd say you really need to look at your needs and your probable water supplies. Make a choice of a filter that is going to fit your destination and water sources. Until then, I'd say I haven't found a perfect all-around water filter yet.
