Great topic here, as commentary has always been one of my favorite parts about pro wrestling. And there's certainly plenty to choose from.
As entertaining as all of the heel commentators (Ventura, Heenan, Lawler, etc.) have been, my favorite is still Jim Ross. I actually kind of idolized Jim Ross as a kid. I always tried to make myself out to be this "know it all" of wrestling trivia as a kid, as I had a gigantic collection of old wrestling magazines, could read passages of the PWI almanacs off the top of my head, could tell people attendance figures and dates and wrestler "heights" and "weights" and all of that stuff. Of course most of what I "taught myself" was all storyline stuff, but I was a kid, what can you expect?
But anyways, I tried to be an "encyclopedia" of wrestling history and stats, and I've always been more of a serious, hard working, perfectionist. I was the "kid that studied religiously for an upcoming test." And Jim Ross to me, seemed like that exact type of person, which he is. Of course JR was playing a character, but you could still tell that even outside his character JR knew his shit. He's famous for bringing up random "facts" about wrestlers (many of which are actually true, such as their college backgrounds, etc.) and stats. JR, as his character, and in real life is a wrestling encyclopedia. To me, he is an expert. He comes across as that in his commentating, and his personal appearances, and interviews, outside of the wrestling business. If I had to pick two people that I could spend the day with and just talk about pro wrestling, the essence of it, what it's about, who was good and great, and just it's history, those two people would be Bret Hart (who would give me the perspective of an actual performer/wrestler) and Jim Ross (who is quite possibly the most passionate wrestling fan in the business. I don't like bbq type foods, but I would still go to JR's restaurant and eat as much of his bbq foods as he wanted me to, just to be able to sit down, hang out with him and talk wrestling all day.
I'm pretty indifferent to people. I don't really "look up to people" or have any real heroes. I've kind of always been my own person, and don't really try to "be like other people." But Jim Ross is someone I respect tremendously and do admire. He's obviously one of the most hard working, no-nonsense people in the wrestling business, which is kind of how I am as a person. You could tell that no commentator was ever more prepared and ready to commentate than JR. If I was an up and coming wrestler, sure I would talk to the veterans that know their shit. But you know what? I'd talk to JR just as much if not more than any of them.
That just touches on my appreciation of him as a human being and the type of person he seems to be. Of course he's also entertaining as hell. He's come up with some of the best catchphrases in wrestling history. And while Jerry Lawler and Paul Heyman were often hilarious while commentating, JR was no slouch and could keep up with them too in the comedic department. JR had said some funny stuff too, especially he when he would argue with them while commentating. That's certainly something that "takes two to tango." You can't have a good argument without both people contributing. So as great antagonists as Jerry Lawler and Paul Heyman were, their jokes and general "assholeness" (new word!) wouldn't be nearly as entertaining if JR didn't react the way he always did.
And I don't think there's a wrestling commentator alive that has as passionate of a voice than JR. Humor and funny lines go a long way, but even more important is passion. A great wrestling commentator is not only supposed to add to the presentation and make it more entertaining (Heenan and Monsoon were masters at this), but is also supposed to tell the story of the match to the fan watching at home. The commentator's job is to make the fan care about what they're watching, especially if the wrestlers themselves aren't able to do that. And I don't think there's ever been a wrestling commentator that was better at this than Jim Ross. No commentator can make a match feel so important and epic as Jim Ross can. With his commentating, Jim Ross has made mediocre matches into being good matches. He's made good matches into being great matches. And he's made great matches into being epic matches. His passion for the product can make a skeleton come alive and care about the match. Jim Ross is the best wrestling commentator of all-time. He isn't referred to as "The Voice of the WWE" for nothing after all.
I know some fans here give him a hard time for messing up lines more frequently in recent years, but frankly I don't care. I'd still rather listen to him commentate over anyone in WWE. He's still the greatest of all-time.
My runner up choice would have to be Bobby Heenan. Lawler was great and witty. Ventura had an excellent commentating voice. But Bobby Heenan was the most hilarious commentator of all-time. And he was a master at putting people over in his commentary. Whether you were a good guy or a bad guy, Heenan made the fan watching at home care and interested in who was wrestling in the ring. He put so many good guys over in the matches, but never got out of character as the most obnoxious jerk walking the planet. He was a master.
Other top choices include Gorilla Monsoon, Jerry Lawler, Mike Tenay, Jim Cornette (I enjoyed his commentary quite a bit actually), JBL, and Vince McMahon (annoying at times, but had an unmistakable and thus great announcing voice. And no one could introduce a wrestler to that audience as good as Vince could).
Great topic.