In the right situation and when it’s done well there’s nothing to beat it.
It’s usually passionate, often persuasive, and can leave a feeling of admiration and even awe in listeners.
It often looks like it’s unscripted, off-the-cuff, in the moment, and much or indeed all of it might be, but that doesn’t mean you can’t think about it beforehand. Preparing some sort of structure in your head can mean you make every point you wish to make, in an order that works.
Indeed the amount of preparation you need to do is directly related to your skill and experience in this regard.
Someone who is really good at this is able to stand up and deliver something top class on the spot. We have all seen it happen, and it can be very impressive.
But I have seen other equally good speeches, undoubtedly from the heart and having the desired impact, but which I found out afterwards were practiced and prepared to the nth degree. That is impressive too for different reasons.
But if you haven’t done it before it can be difficult to imagine yourself doing it. To produce a coherent, passionate speech isn’t beyond anyone however. Find a topic, or person/people that you feel strongly about. Once you have that, then if you are ready to be honest and you are prepared to put in some work, anything is possible.