Why? Do you think that US Presidents make critical decisions "on their feet," without preparation, without lots of input from lots of experts?
That's not the way government works. Presidential decisions, in competent administrations, are made after careful, deliberative work, by lots of staff.
I can think of exactly one kind of scenario where a President would have to make a critical decision instantly ("thinking on her feet"). The President would have about 30 minutes... and frankly, no available option would be a good one, or the "right" one. Moreover, all the options would have been gamed out in advance, many times. Donald Trump or Kamala Harris, or any other President, would probably handle this about equally well (or badly).
It's all the other decisions that a President makes that matter - that define the difference between a competent administration and an incompetent one. We know from experience that Donald Trump is not up to this - he doesn't attract high-quality assistants, and he doesn't listen to good advice when he gets it. We obviously don't have the same amount of knowledge about Harris (as we never do, with a Presidential candidate who has not actually been there), but what we do know suggests that she'll have a solid team around her.
To me, a no-brainer. I'm not inclined to go with the candidate that has the "Viktor Orban Seal of Approval."