I have used both, each for six months at a time. I used the iodine crystals in the refillable bottle. I think it was called Polar Pure or something like that. Haven't seen it on the market for some time. I now use Aqua Mira liquid (we get it as Pristine).

I had no problems with either, but prefer the chlorine dioxide. While I did not mind the taste of iodine, it's nice to not have it, and I'm convinced the chlorine dioxide does a somewhat better job.

But for me, Billstephenson makes the most important point: learn to evaluate water sources. Even on the AT I was able to use water straight fairly often and never suffered for it. But remember that there can always be something you'd rather not know about just around the bend out of sight. If I have any question in my mind, I treat (sometimes with a double dose and for several hours).

best, jcp