I minored in Public Speaking in college, and have spent years speaking to large groups of people along with some radio experience.
With that said, Obama was very articulate and had some excellent speeches in terms of writing, but he lost track of himself every 3 or 4 words and, for me, the patented Obama "uhhh" just broke any and all continuity in his words. He was also not a well versed ad libber, and I think that's the hallmark of a great speaker. Dude was glued to his teleprompter.
1. Obama
2. Bush
3/4. Trump/Biden. They are both horrendous fkr different reasons. I will say though, last night's speech was far better than I expected in terms of execution.