"It depends" or even it "I don't have a favorite, it changes all the time". These answers are both pretty simple and can be used in different contexts.

Hi Labiba. You could say “My favorite emoji changes depending on my mood.” Or something like that. Does that answer your question?

Hi Labiba, If you want to convey the meaning of what you have written in a single sentence, then the below is a possible solution. If anyone asks me what my favourite emoji is, I would answer that I don't like a specific/fixed one as my preference tends to change. :-)