I watched Sabrina The Teenage Witch, a television movie from 1996. And apparently the movie was made before the TV-show, that I've watched 4 seasons of 7 already, and I haven't read the comics and stuff (is there comics, I think there is comics), so I'm only comparing to the series.
I prefer the casting in TV-show. Only good thing about movie's casting was that Melissa Joan Hart was playing Sabrina, because Hart is amazing, and also young Ryan Reynolds (with really stupid hair) as Seth, whose character was not seen in TV-show. But most of the actors were completely different compared to the TV-show.
Also I think few characters changed a lot. I mean Hilda and Zelda's chacters were completely backwards! In the show, Zelda was the more serious one, and Hilda the hilarious one, but in the movie it was other way round, and it was completely weird. Also, Katie Lamore, or whatever her name was, was changed into Libby Chessler. Marnie had the same actress, but she now was Jenny. Also Harvey in the movie was more geeky and outsider, so in the show they took Harvey's adorable character but gave him Seth's popularity. I guess. But Nate Richert will always be the right Harvey for me. Also, SALEM'S VOICE WAS ALL WRONG. And Salem is the most important part of the show, but his part in the movie was so small, and his voice just... Nick Bakay is the only Salem Saberhagen.
Plot wasn't so amazing. So many... stuff. I mean yeah, I've been watching the show so long, that I live in the show's canon, and not in the movie canon. And I don't even know which one is more correct!
Don't watch the movie. Watch the TV-show.