Actually iodine is the most effective tablet, again it infiltrates cell walls of bacteria to stop them dead. But, its not effective on ecoli and I should have mentioned this.
For use in North America, iodine is preferred,, it also has a very long shelf. If traveling overseas in high human waste area, chlorine based is more effective on ecoli but it has a very short shelf life but it will be used more frequent. This is the reason groups going over seas use it as does the military.
Do not scoop water into your bottle cup, etc. if you plan to dink from it. If you do, after you drop iodine, splash some contents around the rim of your bottle cup.
For large groups or lots of water, a pump filter is great but they can and do clog, always prefilter your water. Glacier silt is very hard of filters.
Boiling water to a rolling boil, its debatable on how long to boil from a good rolling boil to 10 mins boil, is the most effective.
Or get water straight off glacier melt and snow pack. It does have an earthy taste.