Well none of those will clean your water without a treatment system. Ozone is used at the end of the treatment train to deactivate viruses but has no residence time, ozone is also added at the end but has a very short life in the distribution system. Personally, after the water treatment process I would add Cl gas to permeate leaving the plant to the customer as Cl can have a residence time of up to usually 5 to 7 days in a distribution system assuming there are little or few organics to reduce the total Cl levels. We use Cl or Chloramination in all our systems. We have tried different disinfectants but they didn’t preform as well. However the problem with Cl is the production of DBPs in the water which we test for all the time.
After Filtration ( Cleaning) I like to see U.V. as you can monitor organic carbon removal by it’s transmittance. A small snort of Cl2, as a Gas, before a Clearwell of 1 hr detention time and you have a product that will be fresh for 5 to 7 days in a tight Distribution system.
I have had the opportunity to work with all the disinfection technologies you have mentioned. As you have mentioned already cost is not an issue, still the question remains as to what contaminant is the water being treated for? Ozone is the best with the highest disinfection strength. For bacteria and viruses UV is the best option. Chlorine is good and the least expensive but it has a small residual time. Also, if one problem with Chlorine is if Ammonia is present in the water then there will be reaction for the formation of Chloroamines (pH dependent). Chloroamines are better disinfection chemical when compared to Chlorine with higher residual time. However, Chloroamines are carcinogenic in nature.