If it is a flippin huge pool, do you have a flippin lot of space to add equipment? And a flippin huge amount of cash to add equipment? What is the chlorine demand for your pool? How long do you run your filtration system? Do you have hard make-up water? Do you want ease of use, and/or ability to handle complex configuration? Use with automation system/controller? When it stops working (and it will, they all do at some point) will you want to attempt to restore it to operation yourself, or call a warranty service tech (got a long warranty?)
I would advise you to use the next few months to download several of the manufacturers owners manuals, and read them to compare/contrast their systems.
Can you understand their basic operation, and how to change the control parameters, or set/remove alarms?
Does the installation and maintenance seem different from the others?
How can you tell if it's working or needs to be cleaned, how do you clean it, and does the cleaning require parts that aren't included?
A lot of my views on these items were discussed in this link "Is there no tech support?" -
http://www.troublefreepool.com/is-there-no-tech-support-t17866.html
It always pays to do your Homework!
Good Luck, and Best Wishes!!!