Since coming to Earth, Castiel has witnessed and experienced many sensations. He has seen movies, listened to music, tasted food and drink. He has discovered that he preferes the scent of liles over roses, and the taste of apples over blueberries. He dislikes most of the music Dean listens to, but he likes the smile that music brings to Dean's face.
Castiel wishes that Dean would smile more often.
The freedom of preference, of choice, has become precious.
Castiel's very existence often hangs in the balance all because of choice. But for every injury, for every exhausting battle, Castiel is grateful because he knows that at the end of the day he gets to decide whether or not he wants to eat a burger and drink a beer, or to sit down and watch a badly scripted television show. Every night Castiel chooses to lie down in bed beside Dean, to worship his body with kisses and his soul with love.
Every night, every day, Castiel chooses Dean. And that is the most precious choice of all.