Mine's a three way tie between my bedroom, my closet, and my living room (although I guess my closet and my bedroom are the same room except that my closet is a walk-in closet).
After living in a dorm room for 2 years, I have realized how much I enjoy the privacy of my own room. Plus, my room is HUGE. I love it. My closet is also huge. It's probably more decorated with things on the walls than my bedroom. I like my closet because it says a lot about my weird, crazy personality with my clothes, random little things, and posters/pictures on the walls and ceiling.
I like the living room also because it has my white baby grand piano. I sat down and played it for the first time in months today and it's amazing how much more relaxed I feel after playing it. My piano is one of my most prized posessions.
My bedroom, It's where I spend most of my time. I can relax, it's where I get my work done, where my game's are, and my recording. My guitar and dock station. Also a cabnit for food and a mini fridge. And obviously the bed for more than one reason!