I have been using the katadyn gravity camp 6L system. Got it for Christmas, have used it about 3 times so far and will use in about a week for my elk hunt. Works great for our needs to fill hydration packs and cooking with.
I have a 10L Katadyn gravity feed for when I have the space, and it works great for multiple people in camp. I really like it.
I also often carry the MSR Hyperflow, which is pump-style filter, when I need to reduce weight / volume. The flow rate of this filter is very good IMO. The manufacturer does caution that you need to prevent the filter element from freezing (I keep in my 1-person tent with me, or if only using a tarp, in my bag).
The Kayadyn Hiker has served me well for years now. No it's not the lightest and yes I have to pump it but I can filter a lot of water with it quickly. I have hunted in groups as large as 6 people. Most of them ask to borrow my Kayadyn eventually. I recently bought an adapter to pump filtered water through my bladder hose and into the water bladder without taking it out of the pack. I really like that.
I use the MSR gravity fed 5 liter, it is awesome. My cousin has the platypus gravity fed, pretty much same thing. they both work great, are simple (less to break than a pump filter....) and are very light. I would recommend a gravity fed filter, for pretty much any circumstance.