I prefer canon above fanon at all times. It's why I did a study-pass through the whole series again in order to familiarize myself with the characters and details of the series before I started writing my own stories. I feel that the world and the characters don't belong to me, I'm just borrowing them and I like to do justice to the original creator's visions. When I first started looking for fanfic, after watching the final episode, I was very disappointed with how cartoon-like most fanon portrayal of the characters was. At least, all the ones I could find online. It's funny that I found, thanks to Entropy_House, old fanzine stories tended to have more well-rounded versions of the characters and closer to canon. I'm not sure why that is. But that goodness for old fanzines.
I really didn't like the way most online stories reduced such rich, complex characters into two-dimensional caricatures that just took one or two characteristics of a character and have those represent everything about the character. Especially for the character of Avon. That annoyed me the most, and made me want to write a portrayal of Avon that actually came from canon, not a distorted cartoon of Avon.
I tend to like the more boring, functional aspects of Avon as well as the occasional snarky bits. For me, it made him much more human and well-rounded. I know a lot of people don't agree and really do see him as some kind of consistently nasty scrooge-like creature who snarked at everyone and dissed everything. Which is fine. We all have our own personal fanons I'm sure we all believe are close to canon.
I used to amuse myself by dropping entire scenes from the series, as is, into stories, just to see if anyone would comment that it sounds so much like Avon, which it was, straight from canon. Surely no one could possibly deny that canon itself wasn't canon. Surely people who loved Avon would recognize his voice, his attitude and words...
Other fics with unrelentingly and blindly sarcastic Avons would get all kinds of comments like...that's just like Avon, or that's doing Avon 'right,' or that's exactly like the Avon I remember...but none for mine, at least not in some forums. Which made me chuckle, because I knew the truth. Actually, that's not quite true. I have had a few people on fanfiction who have been able to identify exactly where I took some scenes from and sent me some nice notes. That really warmed my heart that there were people out there who saw most of these characters the way I did.
But of course, it takes all kinds and that's the beauty of the show.
Has writing fanfiction changed the way I view original source material? I have a great respect for the writers who created some of the best and most complex characters on TV. But I must admit that on subsequent viewings of the show, I am increasingly troubled by the lack of morality and care in the writing, especially in the Blake seasons.