First off, the best BJ starts off with a woman who REALLY is into it. And I don't mean making porn noises and telling me how big I am...but there's a certain eagerness, aggressiveness, guile that a woman gets when she wants to please her man and is intent on doing so.
Now, for me the best position to receive a BJ is with the woman on her back, head propped up on a pillow and her pulling me into her. This has been done to me many times, but the best was when the woman had one hand teasing my anus, the other around my ballsack, and was just taking all of me very slowly, and putting pressure like she was sucking on a lollipop. Then, she would lightly (and I mean lightly) graze her teeth along my shaft. It was the ultimate multi-task BJ - she was stimulating me 3 different ways and I was getting chills...needless to say she finished the BJ and swallowed...then proceeded to lay me on my back, suck me a little more until I was hard again and screwed my brains out.
Best. BJ. EVER.