All of the filters you list will filter bacteria, cysts and floaties out of water. The Sweetwater system adds a chemical to deal with viruses. Whether you need to worry about viruses depends on where you are going; most I've read indicates that the continental US doesn't pose much of a risk of virii; overseas is a different story.

The practical difference between filters is the method used; do you want to scrub a ceramic element, or change a cartridge once in a while? The Katadyn Hiker/Pro have glass fiber/carbon core cartridges, and the MSR filters have a ceramic element that can be field cleaned.