This question always, in my opinion, needs clarifying as to whether it refers to "of today" or "ever."
Today? Well, I went through pretty lengthy obsessions for Alexis Texas and Aletta Ocean but it really has to be Christy Mack.
Ever? I certainly had spells of thinking it was Briana Banks or Tera Patrick but without sounding too much of a cliche, there is no chance I pumped as much spunk to either of them as I did to Jenna Jameson. Her scenes I still watch over and over again and can't imagine ever not popping them on. Dangerous Tides, Priceless and her Virtual blowjob all are probably in my top 5 "most wanked to" hardcore scenes ever. I even bought her book.