Well, having watched both the film and BBC series, I would rate the BBC series better if for nothing else then for the length of time/ space it provides to a complex novel, characters to develop. Highly recommended.
I found the original series so much better than the film. The film was good. I like Gary Oldman but I remember being so disappointed that he shouted at the end. Couldn't imagine Alec Guiness doing that. Very un Smiley.
People who saw The Professional might get the wrong idea here. He raised his voice for a moment, he didn't really shout. :)