I have used Polar Pure Iodine crystals while backpacking for years. Small, light, easy to use and one bottle will treat about 500 gallons, over time. Only drawback is the water needs to be above about 70F degrees to be effective.
I've also used a PUR scout and other water filtration systems. They are great for filling up 5 water bottles quickly from a cold or realy grungy water source and my preferred choice hiking in a group.
There are some micropur mp1 water purification tablets in my nalgene water bottle survival kit but I haven't used them yet.