Note: I've been folowing this question, the first answers given were short and to the point and tended to list only one of each category (Highest voted - Vs - Favourite).
Latterly it has degenerated into a "upvote my several favourites" fest, which is interesting in the way reality TV is interesting (ie. not much) at least to me, I judge not. Therefore I prefer to follow the initial preferred model of answer.
Doesn't mean I'm going to
Some have answered regarding their output on other sites on the network. Personally, I have answered on seventeen sites on the network, should I interpret the question that way, I'd be invalidating it by making it too broad as "favourite" would depend on too broad a context.
I'll give you
Could Finger-Fencing be Fatal?
Is favourite to me because it was the most fun, it made me snigger in the way I might have at primary school.
Almost realistic way to beat entropy
Is my favourite because it seemed to irritate a good many people who demanded that I edit it for length. I liked it long, it told a story.
How can a sapient species build an advanced civilization, while remaining on one continent?
Because I let go of the here and now and just wrote a story (albeit shoddily, briefly and with a well recieved, accepted answer) that's what I love.
My highest scoring is:
Plausible reason for gold-digging ant
It consists of five simple sentences punctuated with two images. It took me less than 5 minutes to compose and would not be beyond the reach of the average 7 year old's comprehension.
There's an implicit question lurking there about the taste of the lowest common denominator - for another day perhaps.
I'd recommend that the OP award accepted answer status to the answerer that manages to justify their answer to this question as their favourite.