In regards to promos, I'd give the edge to Heyman, solely because the art of promos is drastically different compared to Heenan's time.
For the most part, Heenan cut backstage promos, away from the live audience, with limited time. Heyman gets to come out on live TV and gets ample enough time to speak. Big difference in atmosphere and in front of the live audience, you get the sense that he has the crowd in the palm of his hand.
But to Heenan's credit, whether it was 90 or 120 seconds, he made the viewer raise interest because he brought attention to whatever he was involved in and was always able to put over an angle and the opposition with his words, in such a short amount of time. I just think the ability to do that in front of a live audience every week gives Heyman the advantage.
But, Heenan was still a better manager because he got people over and as I said before, he was a "game changer" as a manager. He was more than just a guy at ringside, he was apart of the story. Heyman was initially in WCW but has only recently became a guy that could affect the outcome of the match again.
Now, although I don't overly agree with this post too much, I respect this one massively, your points are valid and have substance and has been said with knowledge, that it's just a matter of opinion really, there is a difference when people comment in regards to a matter of opinion with knowledge, or when they comment cause they don't know different so go with what they know, after seeing both and knowing both well, you can then, and only then ... put a perspective on these kinda things with an opinion, which I respect and that's why I like this post a lot!
But ... I do feel that you have slightly misjudged Heenan's skills to work a crowd, he knew how to do it at ringside so many times, or even while interfering with the wrestlers (including quite often his own talent, such as Andre or Perfect for example), not forgetting how he handled that whole Weasel Suit match against The Ultimate Warrior .... and the way he would deal (and take) the taunts too ... was very admirable, but again, I really do respect your post massively, though just wanted to mention this.
Well put and I respect your opinions, but Heenan was more than capable of performing and controlling a live audience, but as you said the art of promos is drastically different so from that perspective it is comparing apples to oranges.
You made a great point about Heenan's ability to get his point across in such a short period of time. Heyman needs longer to have an equal effect.
Heenan's ability as an outside interference is legendary. When I think of an outcome that a manager had the most direct influence on I will always consider Heenan costing Ultimate Warrior the IC belt ay WM5 at the top of the list.