Would you say D. Trump, H. Clinton and J. Biden were compelling speakers?

Hillary is excellent at speaking. Trump is good. Biden was good years ago but not so much now. 

The key to being a good speaker is to portray the utmost confidence in whatever it is you are selling the listener. It's easy if the listener has already bought in, at this point they don't even have to listen. You are good when you can reach those who where disinterested. A valueable part of learning debate or speaking is exercises where you offer a stance or opinion that isn't yours but part of the exercise because the skill is independant of your enthusiasm or the subject matter. 

Telling people what they want to hear is a very important part of political speaking. The best political speakers are masters of this. Identity politics is built around this idea; a different speech for different people to gain support independently. Stacking the deck like that isn't how you measure your success. "Selling ice cubes to Eskimos" is how you measure your ability to convince or manipulate minds. 

Trump was compelling only to those who were, for whatever reason/s, vulnerable to his brand of chicanery. HRC and Biden, pretty much the same but they aren't completely insane, as is Trump. A truly compelling speaker, IMO, is the Rev. Dr. William Barber. Check him out when you have the time.

Trump was great at passion and emotion; not truth or facts. Hillary is very educated and good at listening. Biden is pretty mellow, which is great in my view. He doesn't need the stage, and he is very concerned about working with both parties (even though the way DC works, the other party will not work with him). 

Trump had a passion for winning and whether you like it or not, had a passion for putting American first in all world negotiations.  I think his passion was good for the country and I think the stupidity of shooting yourself in the foot so the world will say "you're nice" doesn't work (check southern border for example)  I take issue with those who say Bill Clinton's wife is intelligent and Presidential material.  She has done nothing well on her own.  Secretary of state....well aside form burning millions of pounds of jet fuel, what did she accomplish?   Carpetbagger Senator from New York?  Nothing to see here.   We can go to her law career and hear about some criminals she got off, but other than that she married well and that's about it.  Then there is SloJoe Biden who can't put two sentences together and is still waiting for an aid to put the definition on bipartisanship on a cue card for him to read.  Jimmy Carter moves to number 2 of worst presidents of modern time.

Biden is not a great public speaker, but it's interesting because he comes off as so mellow and nonthreatening, it seems easier for him than anyone else to pass major bills. I mean, his stimulus bill is really going to change the country and his infrastructure bill will almost certainly pull blue collar workers back to the Democrats. Clinton was good for those who like to be told stories and like a little intellectual thought as well. Trump was good for the raw emotions, for those who want to get hyped up and angry. Trump is verbal meth for them.

Jessie Jackson was a compelling speaker.    https://www.youtube.com/watch?v=TQl_6buUggM