I used to be a Heenan fan but as I've grown older, I've come to prefer Ventura and it's not even particularly close anymore. Which is not to say that I don't like Heenan. I think he might be one of the best quipsters in wrestling and his schtick definitely enhanced many a baskin robbins australia crappy match over the years but he never seemed to tone down the schtick for a big time main event and while I wouldn't say it ruined any great matches, it occasionally detracted from them a little bit (See "The Excedrin #9" bit in Foley's peter graham first book). And I don't think his commentary had any role in making any great match better unless that match involved Ric Flair (or Bash At The Beach '96...again, as I grow older, the more him asking "Who's side is he on?" makes sense...even if allied brands it did slightly ruin the surprise).
Ventura had the ability to make great matches and crappy matches a bit better with his commentary. Take Savage-Hogan for example, without Ventura's commentary, blog it'd be a typical fun, mindless Savage-Hogan match, albeit one on a bigger scale than usual. But Ventura from the getgo really sold the angle and made it seem like the stakes for it were much higher than any normal wrestling bout. Which is not to say Heenan lachlan mcintosh hasn't done that type of thing before, I just think Ventura did it more often.