There is no best training flat.
What works best for me may injure you.
How much do you weigh?
Are you a heel or forefoot striker?
Do you pronate or supinate?
Do you have high arches or flat feet?
Are your feet rigid or flexible?
You need to go to a good running store and try on a dozen different models. Even then what feels good in the store may not work out on your runs.
I've been running for 40 years and stick with a model that works. Once they change or discontinue that model I might try 7-8 new shoes until I find one I like. And that's even knowing what I'm looking for.
It gets expensive. I've given away more shoes than I've run in.