Pretty much the same. I have a lot of respect for Di'Anno on the early albums, and some of the early stuff Bruce does (as I noted in the live reviews on Justin's "Devil's Dancefloor") just don't sound the same when sung by him. I mean, only Di'Anno can put the psychotic terror into a song like "Killers", or even tone it back to almost ballad land on "Prodigal son". And I think he definitely does "Phantom" justice. But like people here say, had he not been replaced it's probably unlikely Maiden would have become as big as they did. It's hard to equate them with any other band, and I know Sabbath were wildly successful with Ozzy, so the comparison doesn't really stand, but when Dio joined they went in a different, more progressive direction with a lot more melody driving the songs and a shift away from (ahem) satanic styled lyrics. They almost became another band.
Dickinson brought Iron Maiden to the attention of the world, and they had their biggest hit singles and most successful albums with him. In the footage I've seen of Di'Anno live, he just doesn't seem to be feeling it, and he's almost angry with the audience, almost as if he's up there playing despite them, not because of them, as if he has something to prove. Bruce tends to embrace the audience more (not literally, as that would be gay) and draw them in, with shouts like "Scream for me [insert city here]" and so on. He's definitely a better frontman. Even having left Maiden, Di'Anno still doesn't seem to have the stage presence Bruce has.
And I bet he can't fly a 767!
