It's gotta be PlayStation for me. As a kid, I had the choice between a PS2 and an Xbox. I chose the PS2. I eventually moved onto a PS3, which I got for free because it came with the TV that my family got. I had a couple chances to try out the Xbox 360, but I didn't like it.
I'm sure the same holds true for the latest models. Sony's user interface just seems sleeker and simpler to me.