Bottles: Suggested by the organisers as preferable. Major weight saving while running. The big negative is that we would need to fill up regularly. There was one water point advertised at half way and several others of questionable quality along the way. My personal preference here would be the Nathan Elite 2V Plus. Perfect storage space for the majority of runs with stages up to 2h between refuel points.
You can only really answer this question after you consider your water source from which you will refill en route.
Chemicals are the obvious choice. Chemicals are just not ideal in my opinion as they do not offer protection against Giardia and Cryptosporidia (the main pathogens which are likely to give problems). I did consider Aqua Salveo which provides protection against several pathogens but not Giardia and Cryptosporidium.
Filters or a Steripen seem heavy to carry during a race. However if you weigh them up against the extra water then you come about even if not a bit lighter. Then we have the time required of purifying water. Here we have to guess… less water with more frequent refills (lighter weight and having to stop every 1 to 1,5h to purify). I know that once racing I would be very disinclined to stop and deal with a purifier or filter of any kind. Besides I would not have anywhere to put it in my super light bum bag set up.
I intended using Otter as part of my build up run for the Amatola and Skyrun later this year so I thought it would be a good place to run with a pack. This ultimately swung it for me. I filled my bladder with 1,5l of water, threw 2 Zym in and set off. I refilled with the same at halfway. I must admit that the biggest drawback for me was that running with a bag felt significantly warmer than with a bum bag! However I drank way more than I thought I would (may be due to the warm temps or relatively high humidity) and I am not really so keen to deal with gut issues so all of those clinched the deal for me on this one.