I personally think Anita Turner, Steve Frost, and (runs away for fear of the backlash) Gavin Blyth were all worse, although several instances of Emmerdale have been truly awful during Blackburn's tenure.
Despite Emmerdale's self-evident success during Blyth's era, I did not like his work at all and switched off throughout that period. Aaron was a deeply unlikeable and unconvincing character; the Bartons were merely a poster family with little personality and extremely poor acting ability in the Barton sisters especially; although it was time for the Dingles to take a bit of a backseat, they were all but forgotten under Blyth and replaced with, in my opinion, the panto Wylde family who were just all over Emmerdale like a rash. The show lost it's crucial humour, killing off Shadrach was unnecessary and damaging, and characters started to become very isolated, so instead of a community feel, it was like watching 10 different mini-soaps within one big soap.
Blyth's vision of Emmerdale was very specific; subsequently, Blackburn had an extremely hard time resetting the show in his early reign; as a result, a bizarrely large number of cast all went at more or less the same time; one of the show's worst, if not the actual worst, storyline ever came in the form of Jackson's assisted suicide (another Blyth juggernaut), during which time the show was unbelievably miserable.
All of the above is down squarely to Gavin Blyth.
As for Blackburn, yes he has made some terrible errors of judgment - the Spencers hogging the screen in their early days and being utterly obnoxious; Maurel; the elder abuse plot (device); the saviour sibling story given to the wrong set of characters; Debbie acting like an SS guard most of the time; Zak's utterly appalling and vague 'mental illness' plot - etc. etc. But look at the positives - Genhil have absolutely blossomed, not just as a couple but as individual characters; Amy has become much more likeable since last Christmas and has reinvigorated the Pollards; John Barton's death and subsequent aftermath was powerful and well done; the Spencers are patchy but have improved - Ruby and Dan are likeable, Ali's calmed down and Amelia is shaping up to be one of the show's brightest child stars; even Bernice is coming back!
And let's not forget the live ep - perhaps one of, if not THE best episode of Emmerdale ever, which did a great job of making some rather dodgy plots seem compelling, and written and acted beautifully; there are scenes and dialogue in that live ep I will never forget!
So is Stuart Blackburn ED's worst ever producer? No.