Choosing your Water Filter
Pumps: There's two main categories, ceramic filters (like the MSR) and non-ceramic filters (like the Katadyn Hiker Pro). The ceramic filters are great for cleaning in the field, but are often slower to pump and can get clogged up a bit easier. Pumps are great for solo hikers or maybe even 2 people. However, if you are having to use one pump to fill up 4 people, it's a going to be a good long snack stop when you need to fill up. It also helps to have a pre-filter for getting some of the gunk out prior to getting to the main filter. A neckerchief works great for this.
Gravity devices: I believe MSR makes one of these and Platypus as well, I'm sure there's a lot more. These are great for larger groups because you can generally filter multiple liters very quickly. I think the Platypus advertises filtering 4 liters in 2.5 minutes. Cleaning is generally easily accomplished by just backwashing the filter. These are light enough for one or two people to carry. Be sure, if the bags aren't already labeled, to label the source and target bags.
As you sip filters: These are filters that either fit on top of your water bottle or on your outlet hose from your reservoir. They filter as you drink. I've never personally used these, but I would only use it if you knew you were going to be able to fill your water bottle with non-silty water. After hiking in some of the slot canyons in Utah, I wouldn't want to put that murky water in my water bottle then sip on the go. You'd probably end up clogging your filter every third sip. But, pulling water out of a side stream in the Tetons would probably be no problem.
SteriPen: Same as above, you'd want to have some clear water to use this bug zapper type device. I hear rave reviews on these little items. They are light weight, kill everything, but do have some things to consider. 1.) They require batteries. If the juice is gone, you better have a backup, or your boiling water the rest of the way. 2.) You've got to have a wide-mouth bottle to reach the pen into the water. Your Sigg aluminum bottle with the small opening isn't going to work too well with this, unless you dangled down in the container by a string, assuming it will fit through the opening.