Window seat. Every time.
I don't know about you, but once you start to travel a bit you find what your preferences are, how to enjoy from here to there, what becomes normal, and what you will never tire of. For me, it's a window seat. If clouds don't block the view I'm usually glued to the window, watching the ground move on by, watching the planes at the airport, and watching the luggage people toss the bags onto the plane. Even though travel is often filled with hectic, long, frustrating, tiring, and jet lagged moments, I look out the window and realize how amazing it is to see the world from this perspective.
A few years ago I was flying somewhere in the States with my face glued to the window, watching the planes zip around at the airport. The guy next to me leaned over and said, "Is this your first time on a plane?" I replied no, that I had certainly had been on many flights. He replied, "Ah so you're one of those people, me too! You never get tired of this view, looking out the window like a kid." It's true, I never want to get tired of being curious, fascinated, and amazed. And even if I take the same picture as every-human-being-ever flying on a plane, the classic airplane wing, it will always remind me of being a kid glued to the window, fascinated at what they see.