Are you asking which of these sentences is best? Because all of them are equally good, at least to communicate your opinion. Example:
She is the most beautiful woman I know.
I have never known a more beautiful woman.
I have never known a woman more beautiful than her.
All three tell the reader exactly what you think about her. However, if you are writing for effect, or for contextual reasons you want to emphasize different parts of the sentence, each of these can feel different to the reader. Also, with creative writing you might want a character to talk in a certain way, or develop a personal rhythm to your writing, where you naturally choose one of these over the others.
Now is the most uncertain time I have ever known.
I have never known a more uncertain time than now.
I have never known a time more uncertain than now.
Personally, if I am writing an article on the subject, I would pick the third. I like the rhythm of the sentence, and the way it subtly emphasizes now by not revealing the time frame until the end of the sentence. But there is no grammatical reason to pick it over the other two.