My absolute favorite manager of all time was a favorite in this thread, the "Mouth of the South" Jimmy Hart. And Bobby Heenan was a very close second for me. Bobby is, however, my favorite Color Commentator of all time, as he is for a lot of fans.
Now, people probably have to wonder why I pick Hart over Heenan as a manager. I just found Jimmy Hart to be a lot more obnoxious than Heenan. Hart was always running around the ring distracting his opponents with the megaphone, and physically interjecting himself in the matches. He was always distracting the officials. And he always rallied up the crowd and got them into the matches by going around the ring and antagonizing them.
His colorful wardrobe was another huge plus. The guy was a true walking advertisement for his wrestlers, with having his suits airbrushed for each of his wrestlers, and changing his outfits throughout each of the shows. Then, every couple months, he would get all new suits for each of his talents.
He was just a very colorful personality who I enjoyed watching perform, each and every time he appeared at ringside. He also absolutely loved the business. Also, being that each of the managers before his time did not actually stay at ringside for the matches once the bell rang, I believe after listening to his interview on the Greatest Managers DVD, that he actually was very instrumental in the change with managers actually staying at ringside for each of the matches. At least that was the impression I got from his interview on that DVD. And if so, we have him to thank for pushing this idea with Vince, if it was indeed true, as this produced so many fond memories back then.
It's just a shame that Vince is stuck in this mentality of his in that "only what happens in the ring should matter, and there should be no outside distractions that take away from the action, at all." Managers were once a part of the show. And people could watch the managers, and be entertained by their actions, while still watching the action in the ring.
Managers added a whole boatload of variations to match finishes that can't be offered today, since Vince has done away with them. They could interfere and cost the opponents the match. They could have interference that could backfire, and cost their own wrestlers the match. They could get caught by their opponent and get the crap kicked out of them. All of that helped make wrestling so much more interesting than today, when all you have is two wrestlers facing each other all the time.