It's snuggly and warm and convenient. I do probably about 90% of my (non-beta) reading there, and a fair amount of writing, too. I do a lot of rough drafting and outlining in longhand, so I can do it wherever.
Reading and/or writing before bed has been a going to sleep ritual for me since I was a teeny little thing. From grade school upward, masses of notebooks and regular books were stacked beside my bed, so I guess it's kind of always been my favorite place to write.
But I do a lot of writing at my computer desk too (for obvious reasons) so I've grown fond of writing there too.
Guess I'm not all that exciting, but there you go.
What's your favorite place to write? Go to YA Highway to see what others have said, and link your post too!