I use Aqua Mira because it is
1. chemically stable
3. a liquid that allows for variable dosing
Properties 1 and 2 apply to the various chlorine dioxide tablets.
Properties 2 and 3 apply to KlearWater (but I have experienced it loosing efficacy over a long trip, so I know it to be unstable).
Variable dosing is really the main benefit of a liquid, in my opinion. It allows the hiker to consume less chemical per unit of water consumed and carry less chemical for a trip. I suppose one could cut up tablets or use them in more than the recommended volume of water, but this seems impractical compared to measuring the liquid dose.
The following description of Dosing Strategies is from "Ryan Jordan's Comments" on the KlearWater page (www.backpackinglight.com/cgi-bin/backpackinglight/klearwater_xinix_chlorine_dioxide_clo2_water_treatment.html):
The following is not unique to KlearWater, and I use this strategy for Aqua Mira as well. Generally, as you halve the dose, you must double the treatment time for the same efficacy. This is a good way to minimize the amount of chemical you take on a trek. Likewise, if you want your water treated faster, or you are treating a more suspect water source, consider doubling your dosage and/or your treatment time. Generally, I use 1/2 ml of KlearWater per liter (e.g., of clear stream water) and wait 30-60 minutes before drinking it. Before going to bed, I use as little as 1/4 ml of KlearWater per liter, and let the water sit overnight. This strategy allows me to treat about 25-30 liters of water from a full MiniDrop bottle (6+ days of hard hiking on a bottle that weighs 0.5 oz full) and more than 80 liters of water from a full 32 ml KlearWater glass bottle (20+ days, 2.9 oz full). That's a very aggressive approach to extending the range of KlearWater. Generally, if the guidelines are followed, a full 32 ml glass bottle of KlearWater (2.9 oz) will last most hikers a week or more on the trail.