My favourite sitting position also happens to be L and Tamaki Suoh's (but that's not why!). For those of you not familiar with Ouran Host Club and/or Death Note, it's legs pulled up to chest, arms usually around the legs or on top of the knees (that's how I do it, at least).
So, what's your favourite sitting position?
EDIT: Er, sorry. I just started watching Death Note yesterday (I had only seen pictures before), and I realized that L and Tamaki have different positions. L's position is very comfortable, though! I sit with my legs pulled to my chest when I'm at the computer, and I sit in L's position (feet on chair, bottom in the air, body leaning onto the thighs, hands on kneecaps) when I'm in a bigger chair.