My favourite Asana is Janu Sirsasana, aka the head to knee pose. It is so simple to do, too.
The fact that I love to do it is only illustrated by the fact that every time I do it, without fail, two things happen.
The first, very noticeable thing is that I smile every time I move up from the first of two repetitions.
The second is that I always am so very calm inside afterwards.
This is what I love the most about Yoga. The fact that it changes me in more ways than I can count. It is the best gift I have ever given to myself.