Picking only one piece is really difficult, to tell the truth. There is something to that saying about everything a writer creates being our 'darlings' and why it's so difficult to cut them out of something.
We like almost everything we write. We may not like where it ends up and feel that it belongs elsewhere, but we secretly love it all.
But, if I had to pick only one favourite, I would have to say that my favourite piece of writing was a blog post I did on food borne illnesses and how to prevent their spread on cruise ships. It doesn't sound like it would be something that anyone could call a favourite, but it was an article I wrote for a cruise ship line aimed at the professionals in that business.
One of the first things people learn about me is a) I love to sail and therefore b) I love boats.
Being given the opportunity to write for professionals in that industry was an honour.
Granted, the subject matter didn't sound that appetizing but its importance was so crucial--so critical--to that business that the work that went into it and the research had to be on point. My writing had to be on point. Any hint of inaccuracy would be an instant assassination of any credibility to the piece and kill any chance of not only the magazine being taken seriously, but my chances of landing another freelance contract.
Yes, the pressure was there for a notice freelancer, but I rose to it. The piece was published in the magazine and on their website's blog... and I was paid fairly for the article.
So, I would have to say that article, despite the subject being rather unpleasant, was my favourite.