Rating: 4 / 5
I've owned the H20 Amigo for about one year, with most of my use concentrated in Yellowstone and the Tetons during the summer of 2006.
When I'm by myself, I tend to stick to AquaMira because it's lighter, smaller, and, with a good game plan, more simple to use. However, when I'm with one or more people in a group and the focus is on being in camp, the Amigo wins hands down. Run down to the nearest source, scoop up a bunch of water, bring it back, and you've got water for everyone to drink, cook with, shower with, etc.
The filter works very quickly, taking only a few minutes to fill up a 1L bottle as long as it is held/suspended from a height that lets the hose extend completely, and I've never had a problem with the filter clogging or not working. You usually do have to get your hands wet to get the bag far enough under water to be completely full, but if it's cold enough for that to really matter, you're going to be melting snow anyway, not using a gravity filter that will freeze up and become useless almost immediately.
The other way in which the Amigo has its advantages is for "cameling up" at a water source. You can pretty quickly filter out a liter and drink it down while you're filling your other bottles. When you're done, refill that 1L you just drank and you're on your way, hydrated for a long time to come.
My real rating is a 4.5. For me, a 5 would be a version of this filter that comes in closer to 5oz, perhaps with lighter hardwear and a cuben water bag. Filters and chemical treatments each have their advantages, so I don't offer this as being better or worse than AquaMira. But if you've decided that a filter is the right choice for your hiking style and situation, this is the best solution that I've found.